Pound the top round beef steak slices to about ¼-inch thickness using a meat mallet, then season both sides with kosher salt and freshly ground black pepper. Spread a thin layer of yellow German mustard over each slice.

On each mustard-coated beef slice, layer a slice of bacon, a few dill pickles, and finely chopped yellow onion.

Starting from one end, tightly roll each beef slice around the fillings, securing everything inside with toothpicks or kitchen twine.

In a large Dutch oven, heat 2 tablespoons of unsalted butter and 1 tablespoon of olive oil over medium-high heat. Add the rouladen, browning each roll for about 3-4 minutes per side.

Remove the rouladen and add chopped onions, diced carrots, celery, and minced garlic to the remaining fat. Sauté for 5-7 minutes until the vegetables are tender.

Return the rouladen to the pot, then pour in 2 cups of low-sodium beef broth, 2 tablespoons of soy sauce, and 1 tablespoon of tomato paste. Simmer for 1.5 to 2 hours until tender.

Carefully remove the rouladen and strain the broth through a fine-mesh sieve back into the Dutch oven.

Mix 2 tablespoons of cornstarch with 2 tablespoons of water until smooth. Whisk this mixture into the strained broth over medium heat until thickened, about 3-5 minutes.

Slice the rouladen and arrange them on a platter. Spoon the rich gravy over the top, garnishing with fresh parsley.