Cut the onion, carrot and pickle in match-stick style pieces.
Lay out the thin slices of meat and each spread generously with mustard and sprinkle with salt and pepper.
Place bacon on top (if using) and then pickle, carrot and onion along the meat. Roll up tightly and secure with toothpicks.
Heat a large dutch oven or pot over medium-high heat. Add butter or oil. Add cook, turning occasionally, until browned on all sides.
Add 1 cup water or beef broth to the pot and scape up any browned bits from the pan. Cover pot and simmer on low for 2 hours.
Remove Rouladen to a plate and bring juices in the pot to a boil. Thicken with cornstarch dissolved in 1 Tablespoon of water. Taste gravy and add additional salt, pepper, or beef bouillon granules, if desired.
Remove toothpicks from the Rouladen and serve with gravy spooned on top.
Beef for Rouladen: Use top round roast (sometimes called topside or beef round roast) beef for Rouladen, and more importantly, ask your butcher to cut it for you! You want long thin slices about 1/4 inches thick and 6-10 inches long and 4-5 inches wide.Mustard: I've found really great German Mustard at Wold Market.Mushrooms: Could be sautéed and added to (or cooked with) the gravy, if desired. Serve Rouladen with:Spaetzle and Red Cabbage (Rotkohl) or peeled, halved, boiled yellow potatoes, mashed potatoes or rice. Make Ahead Instructions: Raw rouladen can be made ahead of time and stored in the fridge for the next day. Cooked rouladen can be stored in the fridge for several days. Ideally, leave out for half an hour to an hour prior to reheating at 250 degrees for 25 minutes, covered.Freezing Instructions: Rouladen can be frozen raw or cooked. Freeze on a cookie sheet or in a roasting pan, then transfer to a freezer bag or other freezer-friendly container and freeze for up to 3 months. When ready to use, thaw in the fridge overnight.