If you see an au gratin potatoes recipe online that does not have breadcrumbs on top then it is most likely not an accurate representation of potatoes au gratin.
Milk/Cream – I believe heavy whipping cream provides a full fat, full flavor options for potatoes au gratin and is absolutely the best ingredient to use. If using milk, you need to go through the process of making a roux and thickening the milk a bit, kind of like a gravy, before adding it to the sliced potatoes.
Cheese – There are a few options you can use when using cheese. For cheaper alternative cheeses try using Swiss cheese, Parmesan cheese or even Mozzarella cheese. For more expensive full-flavored cheeses use Gruyere or Comté.
Breadcrumbs – Breadcrumbs are incredibly traditional in potatoes au gratin and you can use panko breadcrumbs, or any simple breadcrumb will do.
You can also feel free to use Yukon potatoes as well.
I mix everything first in a bowl to ensure the potatoes are seasoned and coated.
When it’s done cooking in the oven, The outside edges of the pan should be bubbling.
REHEATING POTATOES AU GRATIN: To reheat the potatoes au gratin simply add your desired portion to a pan, cover with foil and bake in the oven at 375° for 20-25 minutes or until hot. In addition, you can simply add them to the microwave and heat until hot.
STORING AND FREEZING POTATOES AU GRATIN: Potatoes au gratin can be stored in the refrigerator covered in plastic for up to 4 days. They can also be frozen covered for up to 2 months. Simply thaw them for 1 day in the refrigerator before reheating them.