Prepare the Beef: Place the top round beef slices on a clean work surface. Use a meat mallet to gently pound each slice to an even thickness of about 1/4 inch. Season with salt and freshly ground black pepper.

Assemble the Rouladen: Spread 1 teaspoon of German mustard over each beef slice. Layer with 1 slice of bacon, a few slices of onion, and a dill pickle slice. Roll up each beef slice and secure with toothpicks or kitchen twine.

Brown the Rouladen: Heat 1 tablespoon vegetable oil in a skillet over medium-high heat. Brown the rouladen on all sides, then remove from the skillet and set aside.

Create the Sauce: Deglaze the skillet by pouring in 1 cup beef broth, scraping up any browned bits. Return the rouladen to the skillet, cover, and simmer on low heat for 1 to 1.5 hours until the beef is tender.

Thicken the Sauce (Optional): Remove the rouladen from the pan. To thicken the sauce, create a slurry with 1 tablespoon flour or cornstarch mixed with cold water, then stir it into the simmering broth. Cook until thickened.

Serve: Carefully remove the toothpicks or twine from the rouladen before serving. Serve warm with a generous ladle of the gravy.