1. Preheat your oven to 375°F. Grease a 9″x13″ baking dish with butter or cooking spray.

2. In a medium saucepan over medium heat, melt the butter. Add the minced garlic and diced onion, and sauté until fragrant and softened, about 3–4 minutes. Stir in the flour and cook for 1 minute.

3. Slowly whisk in the heavy cream and half-and-half. Add the chopped rosemary, smoked paprika, sage, salt, pepper, and nutmeg. Cook the mixture, stirring occasionally, until slightly thickened, about 3–5 minutes.

4. Arrange half of the sweet potato slices in the prepared baking dish. Pour half of the cream mixture over the potatoes. Sprinkle half of the asiago, smoked gouda, and Colby Jack cheeses over the layer.

5. Arrange the remaining sweet potato slices on top, pour the remaining cream mixture over them, and top with the remaining cheeses.

6. Cover the dish tightly with aluminum foil and bake for 40 minutes. Remove the foil and bake for an additional 20–25 minutes, or until the potatoes are tender and the top is golden and bubbly.

7. Allow the Sweet Potato Gratin to cool for 5–10 minutes before serving. Garnish with extra rosemary, if desired.