2 tablespoons neutral oil

3 lb beef chuck roast

3 tablespoons butter

4 yellow onions, thinly sliced

4 garlic cloves, thinly sliced

2 tablespoons Dijon mustard

1 tablespoon Worcestershire sauce

3 tablespoons all-purpose flour

1 cup dry vermouth

6 cups beef stock

2 fresh bay leaves

8 sprigs thyme (tied into a bundle)

Kosher salt and freshly ground black pepper, to taste

1 demi baguette, sliced

3 tablespoons olive oil

4 oz Gruyère cheese, grated

2 tablespoons fresh thyme leaves

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Preheat oven to 350°F (175°C).
Cube and season beef with salt and pepper; slice onions thinly and tie thyme sprigs into a bundle.
Heat neutral oil in a Dutch oven over medium-high heat. Sear beef on all sides until deeply browned; transfer to a plate.
Reduce heat to medium, add butter, and caramelize onions for 30–40 minutes, stirring occasionally, until golden brown.
Add garlic and cook for 1–2 minutes until fragrant.
Stir in Worcestershire sauce, Dijon mustard, and flour; cook for 1–2 minutes.
Deglaze with dry vermouth, scraping up browned bits; simmer 5 minutes.
Add beef stock, season with salt and pepper, return beef to pot, and add bay leaves and thyme bundle.
Cover and transfer to oven; braise for 3 hours or until beef is fork-tender.
Let rest 15 minutes before serving.
For the topping: Brush baguette slices with olive oil, toast in oven 8–10 minutes at 350°F, then top with Gruyère and thyme; broil until bubbly and golden.
Discard herbs from beef, top with cheesy crostini, and serve hot.