For the Beef Stew

• 1½ lbs (680 g) beef chuck, cut into cubes
• 2 tsp coarse sea salt
• 1 tsp black pepper
• 2–3 tbsp olive oil
• 2 tbsp unsalted butter
• 5 large onions, thinly sliced
• 1 tsp brown sugar
• 1 tbsp fresh thyme leaves
• 4 garlic cloves, minced
• 1 tbsp Worcestershire sauce
• 1 tbsp Dijon mustard
• 1 tbsp tomato paste (optional)
• 1 tbsp all-purpose flour
• 2½ cups (620 ml) beef broth or stock
• 2 bay leaves

For the Cheesy Bread Topping

• 1 white baguette, sliced
• Olive oil, for brushing
• 2 tbsp Dijon mustard
• 1½ cups (150 g) shredded Gruyère cheese
• 3 tbsp grated Parmesan cheese
• ½ tbsp fresh thyme, for garnish