Here's how I make them.
6 medium potatoes
Peel potatoes and the onion and slice thinly.
Butter a 9 inch casserole and layer onions and potatoes, alternating as you go.
Melt butter in a saucepan over medium heat and whisk in the flour. Cook 1 minute. Add milk and keep whisking while cooking for 1 more minute,until smooth. Add salt, pepper and a sprinkle of paprika.
Pour sauce over potatoes and top with grated cheese.
You could also grate some cold butter over top as well, about 2 tbsps. Finish with a generous sprinkling of paprika.
Bake at 375 F for 1 hour until potatoes are tender and golden.
These scalloped potatoes are so good. Just like my kids' Mother used to make ; )
And still does.