1. Melt butter; add flour, stirring until smooth.~
2. Add mustard, salt, Tabasco and bean liquid plus milk to make 1 1/2 cups; cook until thick.~
3. Add beans and drained onions.~
4. Place in a greased 1-quart casserole; border with buttered bread crumbs.~
5. Bake in preheated 375'F. oven 30 minutes, or until bread crumbs brown.~