Cooking spray or butter
2 cups heavy cream
2 tablespoons unsalted butter
2 cloves garlic, minced
1 bay leaf
1 teaspoon fresh thyme leaves
1/4 teaspoon ground nutmeg
1 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
3 pounds sweet potatoes (about 4 to 5 medium), peeled and sliced into 1/4-inch thick rounds
1/2 cup shredded Gruyère cheese