This Root Vegetable Gratin is a vibrant, cozy casserole that layers sweet potatoes, parsnips, and beets in a creamy herb-infused sauce, topped with melty Gruyère and Parmesan cheese. The earthy sweetness of the vegetables pairs beautifully with the richness of the cream and the nutty sharpness of the cheese. It’s a perfect side dish for holiday feasts, dinner parties, or a hearty vegetarian main. The colorful layers also make it a showstopper on any table.
Ingredients (Serves 6–8):
Vegetables:
- 1–2 long sweet potatoes (about 2 inches thick), peeled
- 3–4 large parsnips, peeled and trimmed
- 3–5 small beets, peeled
Dairy & Cream:
- 14 tablespoons heavy cream, divided
- 4 ounces grated Parmesan cheese, divided
- 1 ounce shredded Gruyère cheese
Seasonings:
- 1 tablespoon fresh thyme, minced (divided), plus extra for garnish
- 1 garlic clove, minced
- Salt and pepper, to taste
Other:
- 1 tablespoon unsalted butter, softened (for greasing the baking dish)
Instructions:
1. Preheat and Prepare
- Preheat your oven to 400°F (200°C).
- Grease a 3-quart baking dish with softened butter to prevent sticking and ensure even baking.
2. Slice the Vegetables
- Using a mandoline or sharp knife, slice the sweet potatoes, parsnips, and beets into very thin rounds (about ⅛ inch thick).
- Place each type of vegetable in its own bowl to season separately.
3. Season and Coat
- Pour 4 tablespoons of cream over the sweet potatoes and parsnips in their respective bowls.
- Pour 2 tablespoons of cream over the beets.
- Add ½ ounce Parmesan and 1 teaspoon thyme to each bowl.
- Season each bowl with salt and pepper, then toss gently to coat all slices evenly.
4. Prepare the Base
- Pour the remaining ¼ cup of cream into the bottom of the greased baking dish.
- Sprinkle with ½ ounce Parmesan and the minced garlic to infuse flavor from the base up.
5. Layer the Vegetables
- Stack the sweet potato slices and arrange them upright in a row at the top of the dish.
- Follow with a row of parsnips, then a row of beets.
- Continue alternating rows until the dish is filled, creating a striped, colorful pattern.
6. Bake Covered
- Cover the dish with foil and bake for 30 minutes, or until the vegetables begin to soften.
7. Add Cheese and Finish Baking
- Uncover the dish and sprinkle the top with the shredded Gruyère and remaining Parmesan.
- Return to the oven and bake uncovered for another 20–25 minutes, or until the top is golden and bubbly and the vegetables are fork-tender.
8. Garnish and Serve
- Let the gratin rest for 10 minutes before serving.
- Garnish with fresh thyme leaves and serve warm.
Tips & Variations:
- Use a mandoline for even slicing and faster prep.
- Add a pinch of nutmeg or smoked paprika to the cream for extra depth.
- Try different cheeses like fontina, white cheddar, or goat cheese for a twist.
- Make it ahead: Assemble the gratin a day in advance and bake just before serving.
Why You’ll Love This Gratin:
- A stunning, colorful presentation
- Rich, creamy, and deeply flavorful
- Perfect for vegetarians and holiday tables
- Easy to customize with seasonal root vegetables
- Comforting yet elegant
Would you like a protein pairing suggestion or a lighter version with milk instead of cream?