Begin by laying out your thin beef slices on a clean surface and generously spread mustard over each slice. Layer crispy, smoky bacon, tangy pickles, and finely chopped onions on top, concentrating in the center. Carefully roll each slice tightly, ensuring the fillings remain intact, and secure them with toothpicks or kitchen twine for a tight seal.

Heat a Dutch oven over medium heat and add a tablespoon of oil. Once hot, add the rolled rouladen seam-side down and brown for about 3-4 minutes on all sides until they develop a beautiful golden crust. This step is essential for building flavor before the slow cooking begins, so don't rush it!

After searing, carefully add beef broth to the pot, ensuring it covers the rouladen halfway. If using, pour in the red wine for added depth. Bring the mixture to a gentle simmer, then reduce the heat to low, cover, and let it cook for approximately 1.5 hours. The beef should become fork-tender during this time, soaking in all the savory flavors.

Once the Rouladen is perfectly tender, remove them from the pot and set aside on a platter. To create the rich gravy, combine equal parts butter and flour in the pot over medium heat, stirring constantly for about 2-3 minutes until a light roux forms. Gradually whisk in the remaining cooking liquid, simmering until the gravy thickens to your desired consistency.

Slice the tender Rouladen into bite-sized pieces and arrange them on plates. Drizzle generously with the thick, savory gravy for an ultimate comfort food presentation. Pair with traditional sides like Rotkohl or Spätzle, that beautifully complement the Authentic German Rouladen, and enjoy each delicious bite!