01 - Arrange the beef slices on a cutting board; season both sides with salt and pepper. Evenly spread 1 teaspoon mustard over each slice.
02 - On each prepared slice, lay one bacon strip, a portion of chopped onion, and a dill pickle spear.
03 - Carefully roll each beef slice, tucking in the sides as you go. Fasten the rouladen securely with butcher's twine or toothpicks.
04 - Heat vegetable oil in a large Dutch oven over medium-high heat. Sear the rouladen on all sides until well-browned, then set aside.
05 - In the same pot, add chopped carrot, celery, and onion. Sauté for 5 minutes until lightly caramelized. Stir in tomato paste and cook for 1 minute.
06 - Pour in red wine, scraping up any browned bits from the pan. Add beef broth, bay leaves, and dried thyme. Return the rouladen to the pot.
07 - Cover the pot and simmer gently for 1 hour 30 minutes to 2 hours, until the beef is fork-tender.
08 - Transfer rouladen to a plate and keep warm. Strain the braising liquid and return it to the Dutch oven. In a small saucepan, melt butter over medium heat and whisk in flour to form a roux. Gradually add strained braising liquid, whisking constantly, and simmer until the gravy reaches desired thickness.
09 - Remove twine or toothpicks from the rouladen. Slice if desired and serve warm with the prepared gravy.