Melt butter in saucepan.
Add the onion and pepper.
Cook over low heat, stirring frequently for about 10 minutes.
Stir in flour and cook for 1 minute.
Remove from heat and stir in broth.
Return to heat and cook until mixture comes to a boil and has thickened.
Remove from heat and stir in cheese.
Season according to taste and pour over turkey in casserole.
Cover with pastry crust and brush top with beaten egg.
Place on cookie sheet and bake at 450° for 30 minutes.
Reduce temperature to 325° and cook for 30 minutes.