Season the beef chuck with salt and pepper. In a large Dutch oven, heat olive oil over medium-high heat. Add the beef in batches, browning it on all sides for about 8–10 minutes. Remove and set aside, leaving drippings in the pot.

In the same pot, add sliced onions. Cook over medium heat, stirring frequently for about 20–25 minutes, until caramelized. Stir in minced garlic during the last 5 minutes.

Stir in tomato paste with the onions, cooking for an additional 2–3 minutes.

Pour in the red wine, scraping up any browned bits from the pot. Allow to simmer for 3–5 minutes.

Return the browned beef to the pot and pour in beef broth. Stir in thyme leaves and tuck in bay leaves. Simmer for 1.5 to 2 hours.

About 20 minutes before serving, preheat the oven to 350°F (175°C). Slice the bread and arrange on a baking sheet.

Once cooked, remove bay leaves. Adjust seasoning with salt and pepper. Ladle stew into oven-safe bowls or leave in Dutch oven.

Layer the bread slices on top of the stew, then sprinkle with Gruyère and mozzarella cheese.

Bake for 15–20 minutes until the cheese is melted and golden.

Remove from the oven, let rest for a couple of minutes, and garnish with fresh parsley before serving.