In a large bowl, mix together beef, onion soup mix, bread crumbs, egg, and milk.
Form beef mixture into 8 patties.
Dredge the patties in flour to coat
Brown the patties on both sides (You don't have to fully cook them if you don't want to since they'll be cooking for 4 or more hours in the slow cooker, too)
Place the browned patties into the slow cooker, layering them if you need to
In a medium bowl, prepare the Au Juis mixture according to package instructions.
Mix in both cans of cream soup
Pour the mixture over the patties.
Cook on LOW for 4 to 6 hours, or until beef is done.