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