Season the beef slices on one side with salt, black pepper and paprika.
Add mustard and spread to cover the surface. Add 2 slices of ham per beef slice, leaving a small space around the edges before adding 3 sliced pickles. Add sliced onions to cover the empty spots without crowding it.
Preheat oven to 350ºF.
To roll...Starting from the large end, fold in the sides while rolling, keeping it nice and tight. Tie the ends and middle of the rolls with kitchen twine; season with more salt and pepper. In a Dutch oven over medium-high heat, add butter and vegetable oil. When sizzling, add the rouladen and sear on all sides, about 2 minutes. Transfer to a plate while making the gravy.
Reduce the heat to medium and add onions; sauté for 2 minutes, scraping the bottom to dislodge any brown bits.
Add garlic and sauté for 30 seconds. Add red wine, broth, tomato paste, Worcestershire sauce, and thyme.
Stir well, increase the heat to high, return the rouladen along with any accumulated juices and bring to a boil. Cover and transfer to the preheated oven; cook for 1 ½ hours.
Halfway through cooking, remove from the heat and rotate the rouladen. Cover, return the pot to the oven and cook for the remaining time.
When the cooking time is up, transfer the rouladen to a plate and cover with foil to keep them warm.
Increase the heat to medium-high and bring to a full boil. Add cornstarch mixture and stir constantly for 2 minutes.
Reduce the heat to medium and add heavy cream; stir well. Taste and adjust if necessary with salt and pepper. Add mustard and whisk until well incorporated.
Cut the kitchen twine, transfer the rouladen to serving plates and spoon the gravy over. Garnish with fresh chopped parsley and serve with red cabbage and mashed potatoes.