Preheat the oven to 400 degrees F (200 degrees C). Coat a baking dish with cooking spray.

Combine cream, butter, and garlic in a saucepan; bring to a simmer. Off heat, stir in parsley, thyme, sage, rosemary, salt, and black pepper.

Arrange 1/2 sweet potato slices in the prepared baking dish; cover with 1/2 Gruyère cheese. Pour cream mixture on top. Arrange remaining 1/2 sweet potato slices over cream; sprinkle remaining 1/2 cheese on top.

Bake in the preheated oven until golden brown and bubbly, about 30 minutes.