Season the beef steaks with salt and pepper, and top each with a little bit of the bacon, chopped egg, breadcrumbs and chopped watercress, spread in thin layer. Roll the beef up into a log and secure with some kitchen string or toothpicks. Season the outside of the rolls with salt and pepper and toss them in the seasoned flour to coat.
Reheat the skillet with the bacon drippings over medium-high heat. Once hot, add the beef roll-ups to the pan (work in batches if your pan can't hold them all at once) and sear them until golden brown all over, about 5 minutes per side.
Add the red wine and beef stock to the pan. Bring the liquids up to a bubble and cover. Transfer the pan to the oven and cook until the meat is tender, about 45 minutes to 1 hour. When the meat is finished cooking, transfer rollups to a platter and cover with foil to keep warm.
Place a medium-size saucepan over medium heat with the remaining 3 tablespoons butter. Cook the shallots until tender, about 5 minutes. Add the remaining 3 tablespoons flour to the pan and cook for about a minute.
Slowly ladle the juices from the pan the beef was cooked in into the flour-butter mixture, whisking to incorporate. Bring up to a bubble and simmer until the gravy has thickened, 2-3 minutes. Remove the pan from the heat and stir in the Worcestershire, mustard and chopped cornichons or pickles. Season the gravy with salt and pepper.
Plate two rouladen per person with a hearty ladle of gravy on top. Serve with crusty bread or boiled quartered potatoes with chives and warm buttered radishes alongside.