Ingredients:
For the Vegetables:
- 2 medium sweet potatoes, peeled and thinly sliced
- 2 medium parsnips, peeled and thinly sliced
- 2 medium beets, peeled and thinly sliced
- 1 small yellow onion, thinly sliced
For the Cream Sauce:
- 2 tablespoons unsalted butter
- 3 cloves garlic, minced
- 1½ cups heavy cream
- ½ cup whole milk
- 1 teaspoon fresh thyme leaves, or ½ teaspoon dried thyme
- ½ teaspoon salt
- ½ teaspoon black pepper
- ¼ teaspoon ground nutmeg
- ½ cup grated Parmesan cheese
For the Topping:
- 1 cup shredded Gruyère cheese
- ¼ cup grated Parmesan cheese
- 1 tablespoon fresh parsley, chopped
- 1 teaspoon fresh thyme leaves, optional
Instructions:
- Preheat the oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with butter.
- Peel the sweet potatoes, parsnips, and beets. Slice all three vegetables very thinly and evenly so they cook at the same rate.
- Arrange the sliced vegetables in the baking dish, alternating sweet potatoes, parsnips, and beets. Add the sliced onion between some of the layers.
- Melt the butter in a saucepan over medium heat. Add the minced garlic and cook for about 30 seconds until fragrant.
- Pour in the heavy cream and milk. Add thyme, salt, black pepper, and nutmeg.
- Bring the cream mixture to a gentle simmer. Cook for 2–3 minutes, stirring occasionally. Do not let it boil rapidly.
- Remove the saucepan from the heat and stir in ½ cup Parmesan cheese until melted and smooth.
- Slowly pour the cream sauce evenly over the layered vegetables, making sure it reaches between the slices.
- Cover the baking dish tightly with aluminum foil and bake for 45 minutes.
- Remove the foil and check the vegetables with a fork. They should be beginning to become tender.
- Sprinkle the Gruyère and remaining Parmesan cheese evenly over the top.
- Return the uncovered dish to the oven and bake for another 20–25 minutes, until the vegetables are completely tender and the cheese is golden and bubbling.
- Let the gratin rest for 10–15 minutes before serving. Garnish with fresh parsley and thyme.
Nutrition Information (approximately per serving, 8 servings):
Calories: 390
Protein: 11g
Carbohydrates: 35g
Fiber: 6g
Net Carbs: 29g
Sugar: 11g
Fat: 24g
Saturated Fat: 15g
Cholesterol: 75mg
Sodium: 500mg
Nutrition may vary depending on the size of the vegetables, cheese, and cream used.
Nut Information:
- This recipe contains no tree nuts or peanuts.
- It is naturally nut-free when all packaged ingredients are checked for cross-contact.
- Parmesan and Gruyère do not contain nuts, but check labels if preparing this for someone with a severe nut allergy.
Q&A:
Q: Can I prepare this gratin ahead of time?
A: Yes. Assemble the gratin, cover it tightly, and refrigerate for up to 24 hours. Bake when ready, adding a few extra minutes to the covered baking time.
Q: Can I use different root vegetables?
A: Yes. Carrots, turnips, rutabaga, or celery root can be substituted for some of the sweet potatoes, parsnips, or beets.
Q: Do I need to cook the beets first?
A: No. Thinly sliced raw beets can be layered directly into the gratin. Slicing them very thinly helps them cook properly.
Q: Why should the vegetables be sliced thinly?
A: Thin, even slices cook more evenly and become tender without requiring an excessively long baking time.
Q: Can I use regular milk instead of heavy cream?
A: You can, but the sauce will be thinner and less rich. For the creamiest gratin, heavy cream gives the best result.
Q: Can I use another cheese instead of Gruyère?
A: Yes. Swiss cheese, sharp cheddar, fontina, or mozzarella can be used.
Q: How do I store leftovers?
A: Store leftovers in an airtight container in the refrigerator for up to 4 days.
Q: Can I freeze this gratin?
A: Yes, although the creamy sauce may change slightly in texture after freezing. Cool completely, wrap tightly, and freeze for up to 2 months.
Q: What should I serve with root vegetable gratin?
A: It pairs especially well with roasted chicken, beef, pork, turkey, or a simple green salad.