Lay out beef slices on a board and pat dry. Lightly flatten with a meat mallet if needed so each slice is even (about 1/4 inch / 6 mm). Season both sides with salt and pepper.

Spread about 1/2 tbsp Dijon mustard over each beef slice, leaving a small border.

Place one slice of bacon across each beef slice, add a spoonful of sliced onion (reserve the rest), and 1 pickle quarter. Don’t overfill.

Roll the beef tightly from one end and secure with toothpicks or tie with kitchen twine. Set aside.

Lightly dust each roulade with flour — this helps the sauce thicken later. Shake off excess.

In a large heavy pot or Dutch oven, heat oil over medium-high. Add roulades and brown on all sides (about 3–4 minutes per side) until a deep golden crust forms. Work in batches if needed. Transfer roulades to a plate.

Reduce heat to medium. Add butter. Sauté the reserved sliced onions, chopped carrots, and celery for 5–7 minutes until softened and starting to caramelize.

Pour in the red wine (if using) and scrape up browned bits from the bottom — simmer for 2 minutes to reduce.

Add beef broth, bay leaf, and thyme. Return roulades to the pot so they’re partly submerged. Bring to a gentle simmer.

Cover and simmer gently for 1.5 to 2 hours on very low heat, or transfer covered to a 325°F / 160°C oven for 1.5–2 hours. Roulades are done when fork-tender.

Remove roulades and keep warm. Skim excess fat from the sauce. If you like a smoother gravy, strain sauce into a saucepan and simmer to concentrate. Thicken with cornstarch slurry or whisk in a little butter + flour roux until you get desired consistency. Simmer for 5–10 minutes. Season to taste.

Remove toothpicks or twine, slice roulades slightly on the diagonal, spoon gravy over top, and serve hot.