Place beef slices on a cutting board and lightly pound using a meat tenderizer.
Spread a layer of mustard over each piece of meat and season with salt and pepper. Lay bacon and onion on top and finish with a pickle.
Roll up each Rouladen lengthwise and secure with toothpicks.
Heat butter or oil in a pan and brown the outside each roll. Place in a roasting dish or dutch oven, add broth, canned mushrooms (optional) and pickle juice. Roast 90-120 minutes or until fork-tender.
To Make The Gravy
Remove Rouladen from the juices, set aside and cover to keep warm.
Bring juices to a boil. Combine corn starch with water. Whisk the cornstarch mixture into the juices until it reaches desired thickness (There may not be a need for all the cornstarch mixture)
Notes
To save time, purchase beef that has been sliced and tenderized for you.
Batch cook these beef rolls, for quick and easy weeknight dinners. Try cooking them in the crockpot on low for 7-8 hours for a "set it and forget it" method.
Refrigerate leftovers in a covered container for up to 5 days or freeze for up to 6 weeks. A simple trick is to freeze rolls on a parchment lined baking sheet, then transfer them to a zippered bag for long term storage.
Reheat leftovers covered with foil in the oven, on the stovetop or in the microwave. Thaw frozen product in the refrigerator before reheating.