Ingredients
Vegetables
- 1-2 long sweet potatoes (about 2 inches thick), peeled
- 3-4 large parsnips, ends trimmed and peeled
- 3-5 small beets, peeled
Dairy & Cheese
- 1 tbsp unsalted butter, softened (for greasing)
- 14 tbsp heavy cream, divided
- 4 ounces grated Parmesan, divided
- 1 ounce shredded Gruyere
Herbs & Seasonings
- 1 tbsp fresh minced thyme, divided plus more for garnish
- 1 garlic clove, minced
- Kosher salt and pepper, to taste
Instructions
- Preheat and Prepare: Preheat your oven to 400°F (200°C). Grease a 3-quart oval baking dish thoroughly with the softened butter to prevent sticking and add a subtle richness.
- Slice the Vegetables: Using a mandoline or a sharp knife, slice sweet potatoes, parsnips, and beets into very thin rounds. Place each type of sliced vegetable into separate bowls to prepare for seasoning.
- Season Each Vegetable: Pour 4 tablespoons of heavy cream over both the sweet potatoes and parsnips, and 2 tablespoons of cream over the beets. Add 1/2 ounce grated Parmesan and 1 teaspoon minced thyme to each bowl. Generously season each with kosher salt and freshly ground pepper, then toss gently to ensure all slices are well coated with the cream, cheese, and herbs.
- Layer Cream and Garlic in Baking Dish: Pour the remaining 1/4 cup (4 tablespoons) of heavy cream into the bottom of the prepared baking dish. Sprinkle 1/2 ounce of grated Parmesan and the minced garlic evenly over the cream to infuse the base with flavor.
- Arrange the Vegetables: Start by lining sweet potato slices standing up on a bias along one edge of the baking dish. Follow with a row of parsnip slices, then a row of beet slices. Repeat this layering pattern to create six total rows of root vegetables, alternating sweet potatoes, parsnips, and beets until all slices are used.
- Season the Top Layer: Sprinkle the assembled gratin with salt, pepper, and the remaining grated Parmesan. Cover the dish tightly with foil to keep moisture in during the initial cooking phase.
- Bake Covered: Place the covered gratin in the preheated oven and bake for 30 minutes or until the vegetables become soft and start to meld together.
- Add Gruyere and Finish Baking: Remove the foil and evenly spread the shredded Gruyere cheese on top. Return the dish to the oven, uncovered, and bake for an additional 18 to 20 minutes. Bake until the vegetables are fork tender, the cheese has melted, and the top has developed a light golden brown crust.
- Garnish and Serve: Once baked, sprinkle fresh thyme leaves over the top for a fragrant, fresh finish. Serve warm as a flavorful accompaniment to your main dish.
Notes
- To ensure even and thin slices, use a mandoline if available, but exercise caution while slicing.
- If preferred, substitute heavy cream for half-and-half to reduce richness, though the gratin will be less creamy.
- For a nuttier flavor, the Gruyere cheese can be substituted with Emmental or aged cheddar.
- Allow the gratin to rest for about 5-10 minutes after baking to help it set and make serving easier.
- This gratin can be prepared a day ahead; assemble and refrigerate, then bake as directed with an additional 5-10 minutes of cooking time if baking from cold.
- Prep Time: 15 minutes
- Cook Time: 50 minutes
- Category: Side Dish
- Method: Baking
- Cuisine: French
- Diet: Vegetarian
