Lay out the beef slices flat on a work surface.

Spread Dijon mustard and pepper along the length of each slice.

Place sliced bacon, onion, and cornichons on one end of each beef slice.

Roll each slice tightly and secure with twine.

In a cast iron pot, brown the remaining bacon and onions.

Add the rouladen to the pot and brown on all sides over high heat.

If browning in batches, use a separate frying pan.

Once browned, deglaze the pot with whisky or brandy.

Add water and a beef broth cube to cover the rouladen.

Add bay leaf, salt, pepper, paprika powder, and a pinch of sugar.

Bring to a boil over medium heat.

Cover the pot with a lid and simmer on low/medium heat for 45 minutes.

Add sliced mushrooms and simmer for an additional 5-10 minutes.

To thicken the sauce, mix Wondra flour with cold water in a cup.

Add the flour mixture to the gravy and bring to a brief boil.

Stir in sour cream until well combined.

Remove the rouladen from the pot and carefully remove the twine.

Place the rouladen in a serving dish.

Pour the gravy over the rouladen.

Serve with red cabbage, potato dumplings or spaetzle, green beans, or brussels sprouts.