au gratin potatoes recipe

Here's a classic and creamy au gratin potatoes recipe: Ingredients: 4 large potatoes, peeled and thinly sliced 1 onion, thinly sliced 2 cups shredded sharp cheddar cheese 3 tablespoons unsalted butter 3 tablespoons all-purpose flour 1 1/2 cups milk 1 cup heavy cream 1 teaspoon salt