Prepare the Potatoes

1. Preheat Oven: Preheat your oven to 375°F (190°C). Grease a baking dish with butter.
2. Layer the Sweet Potatoes: Arrange the thinly sliced sweet potatoes in overlapping layers in the greased baking dish.

Make the Cream Mixture

1. Combine Ingredients: In a small saucepan, heat the heavy cream, garlic, salt, pepper, and nutmeg (if using) over low heat until warm but not boiling.
2. Pour Over Potatoes: Pour the warm cream mixture evenly over the sweet potatoes in the baking dish.

Add the Cheese

1. Top with Gruyere: Sprinkle the shredded Gruyere cheese evenly over the top of the sweet potatoes.

Bake

1. Cover and Bake: Cover the dish with foil and bake in the preheated oven for 40 minutes.
2. Remove Foil: After 40 minutes, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden brown on top.

Cool and Serve

1. Rest: Allow the dish to rest for 5 minutes before serving to let the layers set.
2. Enjoy: Serve warm as a side dish to your favorite main course.