1.     Steam The Vegetables: Bring an inch of water to a boil in a large pot fitted with a steamer basket. Add rutabaga, celeriac and cook, covered for 8 minutes. Add parsnips, sweet potato and steam until a fork inserted into the vegetables goes in and slides out easily, about 17 minutes. Transfer half of the vegetables to food processor fitted with steel blade attachment.

2.     Cook the Garlic: Melt butter in a small skillet. Add olive oil and garlic and cook, swirling until the garlic is just browned, about 20 seconds. Add thyme (or oregano) and remove from the heat.

3.     Puree the Vegetables: Pour half of the garlic oil mixture over the vegetables and add half of the cream, half the salt and pepper and puree. Scrape sides and continue pureeing until completely smooth. Transfer the vegetable mash to a bowl. Repeat with the remaining steamed vegetables, garlic oil and seasoning. Combine the two batches of pureed vegetables. Serve hot.