Rinderrouladen (Beef Roulades)

Lay out the beef slices on a cutting board. Season with salt and pepper. Spread 1 tablespoon of Dijon mustard evenly over each slice. Cut bacon into thin strips, gherkins into quarters lengthwise, and slice half of the onion thinly. Distribute bacon, gherkins, and onion slices over the beef.

Starting from one end, tightly roll up each beef slice. Secure the roulades with kitchen twine or wooden skewers. Heat vegetable oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Sear the roulades on all sides until well browned. Remove from the pot and set aside.

Chop the remaining onion, carrots, celery, and leek into small pieces. Add them to the pot and sauté until softened, about 5-7 minutes. Deglaze the pot with red wine, scraping up any browned bits from the bottom. Let the wine reduce by half.

Return the seared roulades to the pot. Pour in the beef broth. Bring to a simmer, then reduce heat to low, cover, and cook for at least 2.5 hours, or until the beef is fork-tender. Check periodically and add more broth or water if needed.

Once cooked, remove the roulades and keep warm. Strain the cooking liquid through a fine-mesh sieve into a saucepan, pressing down on the vegetables to extract all liquid. Discard the solids. In a small bowl, melt butter and whisk in flour to make a roux. Bring the strained sauce to a simmer, then whisk in the roux until the sauce thickens to your desired consistency. Season with salt and pepper to taste. Serve the roulades with the gravy.