In dutch oven over medium-low heat, saute the finely chopped onion and bacon together until bacon is translucent but not brown, about 10-15 minutes.
Into bottom of a 6-quart crock pot or slow cooker, place the beef rump roast.
Pour in the (undiluted) can of beef broth and the dill pickle juice.
Over the top of the roast evenly spread the mustard and finely chopped dill pickles (or dill pickle relish). Dot with the whole bay leaves and sprinkle generously with salt and pepper. Top roast with the sauteed onions and bacon.
Cover and cook on high for 6-8 hours, or until tender. Remove meat, and strain juices to make gravy (see to make gravy below).
TO MAKE GRAVY:
Strain juices from roast through a fine mesh strainer into a sauce pan or dutch oven.
Make a slurry in a 2 cup glass measuring cup using a fork to whisk together 1 cup cold water and 1/2 cup flour, until smooth. Pour the slurry all at once into the pan of juices.
Using a wire whisk and whisking all the while, bring the gravy mixture to a boil over medium-high; then reduce to a simmer and continue to cook and whisk another 5 minutes (gravy wil thcken more as it cools).
P.S. Good sides are green beans (Gruene bohnen), sweet and sour red cabbage (Rotkohl), and boiled or mashed potatoes topped with fresh snipped parsley. Guten appetit!