To make this Garlic Scalloped Sweet Potatoes Recipe gluten free, verify that the cornstarch is certified gluten free or labeled gluten free. Confirm that the heavy cream, butter, Parmesan cheese, thyme, salt, and black pepper are free from gluten-containing additives or cross-contact warnings. Sweet potatoes are naturally gluten free. Use clean cookware, utensils, and a clean baking dish to prevent cross-contact with gluten-containing foods.