The primary distinction between scalloped potatoes and potato gratin traditionally lies in the inclusion of cheese; gratin always features a cheesy topping or layers to create that signature golden crust, while scalloped potatoes typically forgo it. Although both dishes use sliced potatoes and a creamy sauce, gratin often employs a richer béchamel base, whereas scalloped potatoes tend to utilise a simpler milk or cream sauce. Ultimately, the addition of cheese in a gratin significantly contributes to its distinctive texture, flavour profile, and the characteristic browned 'au gratin' finish.
