Spread out the beef roulades on a work surface. Massage the oil into each roulade, spread mustard on top, season with salt and pepper, and let rest for 15 minutes.
Mix the bacon, finely chopped pickles, and finely chopped onion together. Spread this mixture over each roulade. Roll each roulade tightly and secure with toothpicks, roulade needles, or string. Coat each roulade with flour.
Heat the clarified butter or lard in a large saucepan over medium-high heat. Fry the roulades, turning to brown all sides evenly, until browned, about 8-10 minutes. Pour in buttermilk until the roulades are just covered. Bring to a boil, then reduce heat to low. Simmer for approximately 2 hours, until the meat is very tender. Taste and season the sauce with salt and pepper as needed.
Serve the roulades with pasta or dumplings such as Bohemian dumplings, and red cabbage on the side.
Cool any leftover roulades and cut horizontally for serving on a cold buffet.