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How to make scalloped potatoes and ham
Preheat the oven to 350 f (177 c) and grease a 2-quart (2 liters) casserole dish with cooking spray.
Melt the butter in a large saucepan over medium heat, then add the onion and cook for 2 minutes.
Stir the onion occasionally to help it cook evenly.
You will be ready for the next step when the onion turns tender. Whisk in the flour, salt, and pepper and cook until it turns smooth and bubbly.