Smoked Bratwurst Casserole

This is a nice winter dinner and very reasonable to make.
5 red skined potatoes sliced thin
1 onion sliced thin
1 package of smoked bratwurst or hotdogs sliced 1''thick
3 tbs. butter
2 tbs. flour
1 1/2 cups milk
salt and pepper
shredded cheese
Met butter in a fry pan add flour stirring to make a roux then add milk and stir till all the lumps are gone
layer the potatoes onions and cheese add the roux and bake 1 hour at 350 degrees
string beans for a side or 3 bean salad feeds at least 6