Wash and clean the casing thoroughly, scraping off the fat with a dull knife and discarding.
Cut into lengths about 8" (20 cm.) and sew one end of each length closed.
In a skillet melt the chicken fat and in this saute the onions until browned.
In a mixing bowl sift together the flour, salt and pepper. Add the melted chicken fat with the onions and the breadcrumbs and mix thoroughly.
Stuff each section of the casing loosely with this filling and sew the second end closed.
Rinse off any flour that adheres to the surface.
Immerse in boiling water for 5 minutes and then drain. (At this point the kishke is ready for use in cholent (see Recipe#269267 ).
To serve kishke alone, arrange the sections in a shallow, lightly greased casserole or baking dish and bake in a medium oven until well browned (about 1 1/2 hours), basting frequently with the drippings.