Traditional Potatoes au Gratin gets a healthy makeover! Parsnip, Potato, and Leek Gratin is made with thinly sliced thin-skinned potatoes, sweet parsnips, mild-flavored leeks and are layered in a decadently luscious lightened-up cheese sauce that is baked until golden brown.

This is the perfect side dish to complement any weeknight meal or special holiday occasion!

slice of parsnip gratin on layered circular white plates.

I originally shared this recipe on December 13th, 2013. I have updated the images and text to share it with you again today.

Why We Love This Recipe for Parsnip Gratin

Here in Vermont, there is a magical nip in the air with the warm and pleasant feelings of the holidays. And between all the hustle and bustle, we are slowly getting together our holiday meal plan. So, this year, we are looking to add comforting, healthy, and hearty dishes to our dinner table.

And one dish that has made its way onto our menu is my Parsnip Gratin. This effortless dish is a lightened-up version of the traditional scalloped potatoes. And while this comforting side may be a lower-calorie, healthier twist on the classic, it is still one savory and decadent dish. Not only is it fancy enough to serve alongside roasted pork loin, ham, lamb, or roast beef at your next holiday get-together but is easy enough to whip up as a perfect side for any weeknight meal.

And we know that many of you have never ventured down the parsnip road before and may have a few questions about this sweet little root vegetable – do not worry, we’ve got you covered! This Ultimate Guide to Parsnips has so many great tips, tricks, and recipes to answer all your parsnip-ity needs!

And in case you’re curious, no, a parsnip is not just a white carrot!

Key Ingredients

parsnip, potato, leek gratin ingredients with text overlay

Parsnip

This recipe calls for 1 pound of parsnips. A good rule of thumb is that 1 pound of parsnips is equal to 4 smalled-sized parsnips or 2 medium-sized parsnips.

When at your local grocer, be sure to pass the big, fat parsnips as they tend to be woodier. Instead, always opt for the firm small to medium-sized ones as these will be subtly sweet with nutty undertones that you are looking for in this dish. Also, be sure to skip any that are limp or discolored.

Potatoes

Use any waxy, thin-skinned potato you may like for this recipe as they are low in starch and high in moisture; meaning they retain their shape when sliced and then baked.

Leeks

Use only the white and light green parts of the leek. I find that their mild onion-like, slightly sweet flavor complements the savory undertones of the dish really well.

Milk

You can use regular milk or lactose-free milk. To keep this lower in calories, we used fat-free (skim) milk, but any type of milk will work.

Garlic

Whole garlic is used to steep in the cheese sauce. Feel free to peel cloves yourselves or buy pre-peeled cloves at your local grocer.

Flour

To thicken the sauce, we used all-purpose flour. For gluten-free alternatives, we suggest using a cornstarch slurry instead of trying to use gluten-free flours.

Mustard

Dijon mustard offers a subtle spicy component to the rich cheese sauce. If you cannot find Dijon or do not have any on hand, spicy brown mustard would be a wonderful substitution as their flavor profiles are extremely similar.

Salt & Pepper

Note that we recommend table salt for this recipe. You may use kosher salt instead, but you will want to double the amount.

White pepper has a distinct earthiness to its flavor that pairs extremely well with the earthy almost musky flavors of the nutmeg in the sauce.

Nutmeg

Ground nutmeg adds a depth of flavor to the cheese sauce. The subtle spicy profile of nutmeg really offers a lovely contrast to all the creaminess of the cheese and milk.

Sourdough Bread

Day-old sourdough is the perfect bread source to make homemade breadcrumbs. This bread is a wonderful option for those who find themselves more sensitive to grains and gluten. While not gluten-free, and should not be consumed by those with diagnosed celiac, those who have grain sensitivities find it easier on their digestive systems to consume in moderation.

It is also a great option for diabetics as it has a low-glycemic-index meaning it will cause a gradual increase in blood-sugar levels versus a spike.

Olive Oil

To make this lower in saturated fat, we used good quality extra virgin olive oil when adding to the bread crumb mixture.

Paprika and Garlic Powder

Used to season the breadcrumb mixture, the paprika is also used to give it a slight color.

Cheddar

Freshly shredded extra-sharp cheddar cheese is used in the cheese sauce and on top of this casserole. We find that full-bodied, tangier flavors of this cheese pairs well with all the rich elements of this dish, however; if you would prefer to use just a sharp cheddar that would be delicious as well.

Parmesan

Freshly grated Parmesan Reggiano is used in the cheese sauce of this casserole. We find that the distinct nutty flavor of this hard Italian cheese pairs well with the flavors of this dish, however; if you are not a fan of this Parmesan, feel free to substitute in Pecorino Romano.

Parsley

To garnish and to give the dish a pop of color, fresh parsley is finely chopped and sprinkled on top. If you are unable to locate fresh, feel free to leave off.

Step by Step Instructions To Make This Recipe

steps showing how to make this recipe

Step 1: Prepare Baking Dish

Preheat oven to 350 degrees.  Coat a 9×13 baking dish with cooking spray.  Set aside.

Step 2: Make Cheese Sauce

In a large saucepan over medium-high heat, add milk and garlic.  Cook until steaming. 

In a medium bowl, whisk remaining milk, flour, mustard, salt, pepper, and nutmeg until smooth.  Add flour mixture to hot milk.  Continue cooking while whisking vigorously until mixture bubbles and thickens.

Remove from heat.  Remove garlic cloves with slotted spoon.  Stir in cheeses and whisk until smooth.  

steps showing how to make this recipe

Step 3: Prepare Potatoes and Parsnips

Using a mandolin or sharp knife, slice potatoes and parsnips into 1/8-inch-thick round slices.

Step 4: Assemble Casserole

In prepared baking dish, spread 3 tablespoons of cheese sauce on the bottom.  Layer one third of potatoes, parsnips, and leeks.  Pour a third of cheese sauce over vegetables.  Repeat with remaining two layers.

steps showing how to make this recipe

Step 5: Bake Dish

Cover dish with a layer of parchment paper and then foil.  Bake until vegetables are tender.

Step 6: Make Breadcrumbs

While casserole is baking, process bread in food processor until it becomes a fine crumb.  Add oil, paprika, and garlic powder until crumbs are evenly moist and orange.  

steps showing how to make this recipe

Step 7: Finish Off Parsnip Gratin

Once vegetables are tender, remove from oven.  Remove foil and parchment paper.  Sprinkle remaining cheddar cheese over the top.  Evenly spread bread crumb mixture over the top. 

Return to oven, uncovered, and bake until golden brown.

Let cool for 15-minutes, top with parsley, and enjoy!

finished parsnip gratin in rectangular white baking dis

FAQ And Expert Tips For This Parsnip, Potato, And Leek Au Gratin

How do I store leftovers?

Leftover parsnip, potato, and leek gratin can be stored it in an airtight container in the refrigerator for up to 4 days.

Can this parsnip gratin be made ahead of time?

This is a wonderful make-ahead dish, making it the perfect side to any weeknight meal or holiday celebration.
To make ahead, prepare assemble casserole per recipe card up to step 4. Do not bake per step 4, instead cover with foil and place in the refrigerator. When ready to serve, continue with the last two remaining steps on the recipe card, keeping in mind that the dish may need any extra 10 to 15 minutes to warm all the way through in step 4.

What is a thin-skinned potato?

Potatoes can be divided into two main categories, waxy and floury.

Waxy potatoes are thin-skinned varieties that include White, Chef, Red Bliss, and Yukon Gold. These potatoes are typified by their thin, smooth skin, creamy texture. Thin-skinned potatoes lend themselves nicely to moist heat cooking methods, such as simmering in soups and stews, boiling, steaming, or mashing for mashed potatoes.

The second category, Russet or Idaho, falls into the floury category. These potatoes have rough, thicker skin, and a light/fluffy/starchy interior, that is perfect for baking, roasting, or other dry-heat cooking methods.

I don’t like the flavor of parsnips; can I substitute another vegetable?

Parsnips have a unique flavor. This winter root vegetable tends to have subtle sweetness that can be laced with undertones of bitterness. For some palettes, this flavor profile is undesirable so feel free to swap out the following for parsnips: turnips, rutabaga, celery root, or even sweet potato. Or simply skip them and use more potatoes!

More Recipes To Try This Season

This simple Turnip Casserole is an effortless recipe to keep in your repertoire! Thinly sliced turnips are layered with savory caramelized onions, creamy bechamel sauce and Parmesan cheese. It makes a great side dish to serve with roasted meat and poultry or for an elegant holiday meal.

My gluten-free and paleo Roasted Parsnips are simply prepared but are so delicious. Ready within 30 minutes, this quick dish is the perfect side to any main dish.

This Carrot and Parsnip Mash is paleo-friendly Irish side dish. The sweet and creamy mashed veggies are the perfect side along a hearty, meaty, main course.

parsnip gratin on circular white plate with fork

Thanks so much for reading. If you are new here you may want to sign up for my free weekly email newsletter for healthy recipes delivered right to your inbox. Or follow me on Instagram. If you make this recipe, please come back and leave a star rating and review! It is very appreciated. Happy Cooking! ~Katie

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parsnip gratin in white casserole dish

Parsnip, Potato and Leek Gratin

  • Author: Katie Webster
  • Prep Time: 25 minutes
  • Cook Time: 2 hours
  • Total Time: 2 hours
  • Yield: 12 1x
  • Category: Side Dish
  • Method: Oven
  • Cuisine: American

Description

Light scalloped potato or potato gratin recipe with parsnips, leeks and extra sharp cheddar. This is a wonderful make-ahead dish, making it the perfect side to any weeknight meal or holiday celebration.


Scale

Ingredients

  • 2 ¼ cup low-fat milk, divided
  • 2 cloves garlic, crushed and peeled
  • 1/3 cup all-purpose flour
  • 1 tablespoon Dijon mustard
  • 1 teaspoon salt
  • ¼ teaspoon ground pepper, preferably white
  • pinch nutmeg
  • 6 ounces shredded extra-sharp cheddar cheese, divided (1 ½ cups)
  • 2 ounces shredded Parmesan cheese (1/2 cup)
  • 3 pounds thin-skinned potatoes
  • 1 pound parsnips, peeled (about 2 medium)
  • 2 medium leeks, thinly sliced and washed
  • 2 slices bread, preferably sour-dough or mild whole wheat, crusts removed if desired
  • 2 teaspoons extra-virgin olive oil
  • ½ teaspoon paprika
  • ¼ teaspoon garlic powder
  • 2 tablespoons freshly chopped parsley

Instructions

  1. Preheat oven to 350 degrees F. Coat a 9 by 13 baking dish (or similar size) with cooking spray.
  2. Heat 1 ½ cup milk and garlic in a large saucepan over medium-high heat until steaming.  Whisk the remaining ¾ cup milk, flour, mustard, salt, pepper and nutmeg in a medium bowl until smooth.  Whisk the flour mixture into the hot milk and continue cooking, stirring often until mixture bubbles and thickens, about 7 minutes. Remove from the heat and remove garlic cloves with a slotted spoon. Stir in 4 ounces (1 cup) cheddar and Parmesan. Whisk until smooth.
  3. Slice potatoes and parsnips into 1/8-inch slices using a mandolin or sharp knife.
  4. Spread 3 tablespoons of the cheese sauce into the bottom of the prepared dish. Layer in one third of potatoes, parsnips and leeks. Pour about one third of cheese sauce over the vegetables. Repeat with a two more layers of vegetables and cheese sauce.
  5. Cover with a layer of parchment and then foil, and bake until the vegetables are tender, 1 hour 40 minutes.
  6. Tear bread into pieces and process in a food processor until it becomes fine crumbs. Add oil, paprika and garlic powder and process until evenly moist and orange.
  7. Remove foil from the gratin. Sprinkle the remaining 2 ounces (1/2 cup) cheddar over the top. Spread the bread crumb mixture over the top. Return to the oven and continue baking until golden brown, about 20 minutes longer. Let cool fifteen minutes before serving topped with parsley.

Notes

Serving Size

The serving size here is really generous, so if you’re serving several side dishes, this will serve more like 15 or 16 people!

Make Ahead

To make ahead, prepare assemble casserole per recipe card up to step 4. Do not bake per step 4, instead cover with foil and place in the refrigerator. When ready to serve, continue with the last two remaining steps on the recipe card, keeping in mind that the dish may need any extra 10 to 15 minutes to warm all the way through in step 4.


Nutrition

  • Serving Size: 1/12th casserole
  • Calories: 224
  • Sodium: 414
  • Fat: 6 grams
  • Saturated Fat: 4 grams
  • Fiber: 3 grams
  • Protein: 11 grams
Parsnip Potato Gratin