1. Slice the onions

• Trim the top ends of the onions, but keep the root ends intact so the halves stay together.

• Peel off the outer skins.

• Using a mandoline or sharp knife, thinly slice the onions (you’ll want uniform slices for even caramelization).

2. Sear the beef

• Pat the beef cubes dry with paper towels, then season with coarse sea salt and fresh black pepper.

• Heat olive oil in a large Dutch oven or heavy casserole dish over high heat.

• In batches, sear the beef until nicely browned on all sides. Don’t overcrowd the pan—this ensures a good crust forms.

• Transfer browned beef to a plate and set aside.

3. Deglaze with Marsala

• Pour ¼ cup (60 ml) of Marsala into the hot pan, scraping off browned bits from the bottom (fond).

• Let it simmer a few minutes until the alcohol cooks away and the liquid reduces slightly.

4. Caramelize the onions

• Reduce heat to medium-high, melt butter in the same pan.

• Add all sliced onions, pinch of salt, and brown sugar.

• Stir frequently; cook until onions begin to brown (10–15 minutes).

• Stir in minced garlic and fresh thyme, then add the rest of the Marsala.

• Cook, stirring occasionally, for another 20–30 minutes until onions are very soft, richly colored, and sweet.

• Reserve a few spoonfuls of onions for garnish.

5. Build the stew and braise

• Reduce oven temperature to 320 °F (160 °C).

• In a small bowl, mix Worcestershire sauce, Dijon mustard, tomato paste (if using), and flour.

• Add this mixture to the pot, stirring well to coat onions.

• Gradually stir in beef broth, bring to a simmer.

• Return browned beef (and any accumulated juices) to the pot. Add bay leaves.

• Cover and transfer to the oven. Braise for about 90 minutes, or until beef is ultra tender.

6. Assemble and finish

• Remove bay leaves. Give the gravy a taste and adjust the seasoning with salt and pepper as needed.

• Preheat your broiler (or grill) function.

• Spread baguette slices with Dijon mustard, then top with Gruyère and Parmesan.

• Divide the stew into six oven-safe bowls. Top each bowl with one or more cheese‑topped bread slices (you can layer extra cheese over them).

• Place under the broiler just until cheese bubbles and begins to brown—watch carefully so it doesn’t burn.

• Sprinkle with fresh thyme and the reserved caramelized onions before serving.