Scalloped Potatoes

I don't remember where I got this recipe, but I do remember it was really good.
I doubled it and put it in a 9 x 13 pan)

4 c. thinly sliced potatoes (about 4 med.)
3 Tblsp. butter
3 Tblsp. flour
1 1/2 c. milk
1 tsp. salt
1 dash cayenne pepper
1 c. grated x-sharp cheese
1/2 c. more to spread on top
paprika

In a small saucepan, melt the butter and blend in the flour and milk and let it cook for a few minutes stirring with a whisk.  Season with salt and cayenne.  Cook sauce on low till smooth and boiling, stirring occasionally with a whisk.
Reduce heat and stir in the cheese.  Place 1/2 of the sliced potatoes in a lightly greased 1 qt. casserole dish.
Pour 1/2 of the cheese sauce over the potatoes.  Repeat with the 2nd layer of potatoes and cheese sauce.  Sprinkle with the remaining cheese and top with a sprinkle of paprika for color.
Bake uncovered for about 1 hour at 350 degrees or 1 1/2 hours if doubled.