Pound the beef slices lightly to tenderize and cut the pieces of bacon, if needed to be a little shorter than the long length of the pieces of beef. Thinly slice the onion and cut the pickles into matchstick lengths.
Spread each of the slices of beef with a thin layer of mustard. Top each with a slice of bacon then place a few pieces of onion and pickle towards one end. From the end with the onion and pickles, roll up the beef tightly so all of the fillings stay inside then secure the end with a cocktail stick, or alternatively tie two loops of twine around the roll.
Preheat the oven to 325F/165C.
Warm the butter in an ovenproof dish with a lid large enough to hold all of the rouladen in a layer, over a medium-high heat. Brown the beef rolls on all sides well, turning as needed to brown the other sides. If your dish doesn't have a lot of space, brown in batches. Remove the beef rolls from the pan once done and set aside.
Deglaze the pan with the the red wine, scraping any of the browned bits from the bottom (they help add flavor). As it starts to simmer, add most of the water (or stock) and warm through. As it starts to simmer, add back the beef rolls, and a little salt and pepper, cover the dish with the lid and place in the oven.
Cook the rouladen in the oven for around 90 minutes, turning now and then so they don't become dry on any one side. If the liquid becomes too low, top it up slightly.
Once cooked, remove the beef rolls from the cooking liquid and set aside to keep warm. Mix the cornstarch with a tablespoon of water and add to the cooking liquid. Warm over a low heat and stir to thicken into a gravy, then remove from heat.
Remove the cocktail sticks from the rouladen before serving then drizzle over the gravy.