This Sweet Potato Gratin is spiced with rosemary, thyme, and nutmeg, and coated in a dairy-free cheesy sauce for a hearty and cozy dinner side.
- 2 pounds (910 g) sweet potatoes (about 2 medium sweet potatoes)
- 2 tablespoons nutritional yeast
- 2 tablespoons arrowroot powder or cornstarch
- 2 ounces (57 g) dairy-free parmesan cheese*, grated
- 1 tablespoon olive oil
- 3–5 cloves garlic
- 1/2 teaspoon ground nutmeg
- 1/2 teaspoon black pepper, or to taste
- 1 teaspoon salt
- 1 3/4 cups (415 ml) full-fat oat milk*
- 3 sprigs of thyme, leaves de-stemmed
- 1 teaspoon finely chopped rosemary
- Prep: Preheat the oven to 400F and lightly grease a a 9″ oval baking or gratin dish (or similar sized) with nonstick cooking spray. Set aside. Peel your sweet potatoes, then use a mandoline to slice them as thin as possible; I sliced mine to about 1/8 inch. Place the sweet potatoes in a large bowl, then set aside.
- Make the Sauce: Add the nutritional yeast, arrowroot powder, vegan parmesan, oil, garlic, nutmeg, pepper, salt, and milk to a high-speed blender. Blend on high for 45 to 60 seconds, or until a uniform sauce forms. Pour the sauce mixture over the sweet potatoes and add in the thyme and rosemary. Use a spatula (or your hands) to mix well, making sure each piece is evenly coated. Mixing the sweet potatoes ahead of time ensures better flavor and sauce distribution.
- Arrange & Bake: Use your hands to transfer the sweet potato wedges into your baking dish. For the best gratin texture, it’s best to form “stacks” or columns of potato slices, then to lay them into the dish (see recipe notes or video for more details). Place the gratin in the middle rack of the oven and bake for 55-60 minutes, until the sauce is bubbly, but firm.
- Serve: Remove the casserole from the oven and let sit for 5 minutes before serving, to allow the sauce to set. Serve warm; leftovers will keep in the refrigerator for up to 5 days, or can also be frozen for up to 2 months.
- Parmesan: I like to use Violife parmesan cheese for this recipe and grate it myself, but another brand of shredded cheese should work too. If you have a high-powered blender (like a Vitamix) you only need to chop your cheese, not grate it.
- Milk: oat milk can be replaced with lite coconut milk, or a creamy homemade nut or seed milk.