Place the thinly sliced top round beef steak between two sheets of plastic wrap and pound with a meat mallet until about ¼ inch thick. Season both sides generously with kosher salt and black pepper, then spread a thin layer of yellow German mustard over each slice. Layer on crispy bacon, dill pickles, and finely chopped yellow onions right down the center of each beef slice.

Starting from the end with the pickles, tightly roll each slice of beef like a burrito, ensuring the filling stays inside. Secure the ends with toothpicks or kitchen twine. Set aside.

In a Dutch oven, heat a combination of unsalted butter and olive oil over medium-high heat until shimmering. Carefully add the rouladen, browning on all sides for about 8-10 minutes.

Using the same pot, add more butter if needed and add the chopped yellow onions, diced carrots, diced celery, and minced garlic. Sauté for about 5-7 minutes until tender.

Stir in soy sauce, beef broth, and tomato paste into the sautéed vegetables, bringing to a gentle simmer. Return the browned rouladen to the pot.

Cover with a tight-fitting lid and reduce the heat to low. Allow to simmer gently for 1.5 to 2 hours.

Carefully remove the rouladen and strain the cooking liquids through a fine-mesh sieve. In a separate bowl, whisk cornstarch and water to form a slurry, then stir back into the strained broth, simmering until thickened.

Plate the beef rouladen and pour the thickened gravy over them. Optional: sprinkle with freshly chopped parsley.