Both scalloped potatoes and potatoes au gratin consist of sliced potatoes baked in a creamy sauce and topped with crunchy crumbs, so you'd be forgiven for mixing up the two. Au gratin, by definition, means "covered with breadcrumbs or cheese and then baked until brown," while scalloped potatoes refers to tubers that have been baked in a creamy sauce and covered with seasoned bread or cracker crumbs. The big difference between the two, then, is the cheese component.
When making either scalloped or au gratin potatoes, choose a tuber that holds its shape and firmness when baked in a creamy liquid, such as a red or Yukon gold potato. While many recipes called for russet potatoes, cooking website The Kitchn suggests that this classic 'tater falls apart after being cooked in a scalloped or au gratin dish.
A standard recipe for creamy potatoes au gratin, such as the dish served at Ruth's Chris Steak House, calls for peeled potatoes combined with heavy cream, milk, flour, garlic, butter, cheddar cheese, salt and pepper, plus a sprinkling of chopped fresh parsley for garnish. Create interesting variations on the side dish by varying the cheese used. Options include:
- Stilton, if you like the strong favor of blue cheese
- Gouda, for a smoky flavor
- Pepperjack, for a bit of spice.
Add extra intrigue by sprinkling in chopped cooked bacon or replacing half the sliced potatoes with rutabagas or turnips.
Because scalloped potatoes don't call for any cheese, the recipe is a bit simpler than potatoes au gratin.
Simply combine sliced potatoes with butter, heavy cream, whole milk and a bit of grated nutmeg, plus salt and pepper to taste. Sprinkle buttered breadcrumbs on the top before baking. To add a little more intrigue, try a variation:
- Replace standard potatoes with sliced sweet potatoes.
- Add a tablespoon of horseradish to the sauce for a little kick.
- Sprinkle in diced ham and chopped bell peppers to make it a main dish, whether for breakfast or dinner.
Although, by definition, scalloped potatoes recipes don't call for cheese, and both scalloped and au gratin potatoes can use breadcrumbs on the top, many recipes add cheese to scalloped potatoes or eliminate the breadcrumbs entirely -- hence perpetuating the idea that the two dishes are interchangeable.