Pound the beef: Lay each beef slice between plastic wrap and gently pound to about 1/4 inch (6 mm) thick. Season lightly with salt and pepper.

Spread mustard: Spread about 1/2 tbsp mustard over each slice, leaving a 1/2-inch border.

Add filling: Place 1 bacon slice (or folded turkey bacon), a tablespoon of chopped onion, and one pickle spear near the short edge of each slice.

Roll tightly: Roll each slice tightly away from the filling and secure with toothpicks or kitchen twine.

Brown the rouladen: Heat oil in a large skillet or Dutch oven over medium-high heat. Brown rouladen on all sides, about 2–3 minutes per side, until well caramelized. Work in batches if needed.

Deglaze the pan: Remove rouladen briefly to a plate. If using wine, pour it into the hot pan and scrape up browned bits (deglaze) — simmer 1–2 minutes. If not using wine, skip to the next step.

Add braising liquid: Return rouladen to the pot, add beef broth, bay leaves, and thyme. The liquid should come about halfway up the rouladen. Bring to a gentle simmer.

Braise: Cover and transfer to a preheated oven at 325°F (160°C), or simmer gently on the stovetop over very low heat. Braise for 1.5 to 2 hours, until the beef is fork-tender. Tip: check at 90 minutes — if still firm, continue until tender.

Make the gravy: Remove rouladen to a warm plate and skim excess fat if needed. Discard bay leaves and thyme stems. Mix 1–2 tbsp flour with cold water to form a slurry (or 1 tbsp cornstarch with 2 tbsp cold water for gluten-free). Stir into simmering sauce and cook 3–5 minutes until thickened. For richer gravy, whisk in butter at the end.

Return rouladen to the sauce or plate and spoon gravy over top. Garnish with chopped parsley. Serve hot with mashed potatoes, spaetzle, buttered noodles, or a big scoop of braised red cabbage.