Melt butter and shortening in top of double boiler
Add onion let simmer over direct heat about 15 minutes or until onion is very tender but do not brown or burn it
Take pan from heat let cool a moment then stir in flour
Be careful the butter mixture is not too hot or the flour will get lumpy
Stir milk in gradually making smooth
Add and stir seasonings
Place over boiling water and stir constantly until sauce is thickened and well blended Pour this thick sauce over the picked over crab meat
Mix well and refrigerate overnight
Shape the chilled mixture into patties about 1 inch thick
Roll them in the fine breadcrumbs to coat all over and lower them carefully into hot fat deep enough to cover them completely and fry to a deep golden brown
Lift out with slotted pancake lifter and let them drain a moment on absorbent paper