Well, if you want the official culinary definition, scalloped potatoes are typically thicker sliced potatoes baked in cream. No cheese is added. Potatoes Gratin, with au gratin translating to a dish topped with cheese and breadcrumbs in French, are potatoes with those exact toppings. Note that gratin potatoes are often sliced a bit thinner than scalloped potatoes. But like with these cheesy scalloped potatoes, the rules are broken all the time. Though my "scalloped potatoes" might be more appropriately named potatoes gratin, call them whatever you want! This is one rich and creamy side dish you'll want on your menu ASAP