Start with your beef flank or round steak. Cut it into long, thin slices, about 1/4 inch thick. Gently pound the slices to tenderize them further.

Lay each slice flat and spread a thin layer of mustard across the surface. Season with salt and pepper. Place a slice of bacon, a few pieces of onion, and one or two pickles at one end of the beef slice. Roll it up tightly and secure with kitchen twine or toothpicks.

Heat the oil in a large skillet over medium-high heat. Sear the rouladen on all sides until they take on a beautiful brown color, about 3-4 minutes per side.

Transfer the rouladen to a Dutch oven or deep pot. In the same skillet, add some additional onions and any leftover bacon. Sauté until golden, then pour in the beef broth.

Pour the broth mixture over the rouladen in the pot. Add carrots and celery for added flavor. Bring to a boil, then reduce the heat to low, cover, and let it simmer for 1.5 to 2 hours until the beef is tender.

Once the rouladen is fully cooked, remove from the pot and let rest. Strain the cooking liquid, and return it to the pot. Reduce over medium heat until the gravy thickens, adding salt and pepper to taste.

Serve each roulade sliced, drizzled with the rich gravy, and accompanied by your favorite sides.