Prepare stuffing: Peel and halve hard-boiled eggs. Cut the soft sausage into thin strips. Cut the pickles in half or quarters lengthwise, depending on how big they are. If the ingredients are too large, simply trim them when filling the beef slice.
Use a meat mallet to tenderize the beef cuts on both sides gently. The final result should be a slice of meat that is twice as long as it is wide and no thicker than ¼ inch.
Season the beef with salt and pepper on both sides. Slather one side with a layer of mustard. On the top half of each piece of steak, spread half of a boiled egg, a piece of bacon, soft sausage, an onion wedge, and pickles.
Roll the meat slowly from top to bottom, tucking in the sides. Finally, tie it thoroughly with kitchen twine. Don't be afraid to tighten the string a little. The meat will shrink during cooking, and the contents of the roll could fall out.
Sear the meat: Heat the lard in a saucepan (I used my time-tested cast iron casserole) over medium-high heat and brown the beef rolls on all sides.
Make a gravy: Transfer the browned steak rolls to a plate and add the onion and bacon to the pan with the browned bits. Turn the heat down to medium and cook the onions, stirring them often, until they are golden, which will take about 5 minutes. Add the flour and stir for a further 1 minute.
Add the remaining mustard and stir. Add the pickle brine and beef broth and stir. Return the meat to the pan, bring to a boil, reduce the heat to low, cover with a lid and slowly cook for 1½ hours or until fork tender.
Take the finished roll ups out, remove the string, and set the meat aside on a plate. Season the gravy with salt and pepper and mix it briefly with an immersion blender. Return the ptacky rolls to the sauce and let them warm through.