Sweet Potato Gratin by Delish

 3 Tablespoons unsalted butter, softened, divided, plus more for foil

4 tsp, cloves garlic, chopped

2 Tablespoons, chopped fresh thyme leaves, plus more for serving

1 Tablespoon chopped fresh sage leaves

Kosher Salt

1 cup heavy cream

3/4 cup milk

1/4 teaspoon ground cinnamon

1/4 teaspoon nutmeg

2 large eggs

3/4 cup finely grated Parmesan

Freshly ground black pepper

2 lbs. sweet potatoes, peeled, sliced 1/8 inch thick

2 2/3 cup shredded Gruyere, about 8 ounces

1.Preheat oven to 375. Grease a 1-quart casserole or gratin dish with 1 tbsp. butter. In a small saucepan over medium heat, melt 2 tbsp. butter. Add garlic and cook, stirring, until fragrant, about 1 munite. Add thyme, sage and 1/2 tsp salt and cook, stirring until heated through, about 30 seconds. Add cream, milk, cinnamon and nutmeg. Bring to a simmer, cook, stirring until thickened, about 5 minutes. Remove from heat.

2. In a medium bowl, beat eggs. Transfer 1 cup cream mixture to a liquid measuring cup. Whisking constantly, slowly stream cream mixture into eggs. Add egg mixture to saucepan with remaining cream mixture and whisk to combine. Whisk in 1/2 cup Parmesan.

3. Line bottom of prepared dish with a layer of potatoes; season with salt. Top with 2/3 cup Gruyere and 2/3 cup egg mixture. Repeat 3 times, ending with egg mixture. Top with remaining 1/4 cup Parmesan.

4. Cover dish with buttered foil and bake 30 minutes. Uncover and bake until golden brown, about 30 minutes more. Top with thyme.