Slice two large onions into thin, even strips and cube about two pounds of chuck steak into bite-sized pieces and mince four cloves of garlic.

Heat a tablespoon of olive oil in a Dutch oven over medium-high heat. Season the cubed chuck steak with coarse sea salt and black pepper, then add to the pot. Sear the meat for 5-7 minutes until browned on all sides.

In the same Dutch oven, add two tablespoons of unsalted butter along with the sliced onions and a pinch of salt. Sprinkle in a teaspoon of brown sugar to encourage caramelization. Stir regularly for about 30 minutes.

Once the onions are caramelized, stir in the minced garlic, two tablespoons of Worcestershire sauce, one tablespoon of Dijon mustard, and two tablespoons of tomato paste. Cook for an additional minute.

Return the browned beef to the pot. Sprinkle three tablespoons of flour over the mixture and stir to coat evenly. Gradually pour in about four cups of beef broth and one cup of Marsala wine.

Add two bay leaves and a teaspoon of fresh thyme to the pot. Bring the mixture to a gentle simmer, then partially cover and cook for about 90 minutes.

Preheat your oven to 400°F (200°C). Slice a baguette into thick rounds, brush with olive oil and spread a thin layer of Dijon mustard on each slice. Top with shredded cheeses.

Remove the bay leaves from the stew before serving. Ladle the stew into bowls and place a cheesy bread slice on top of each serving.