Prepare the Beef: Pat the beef joint completely dry with paper towels. A dry surface is crucial for getting a good sear. Season it generously all over with salt and freshly ground black pepper.

Sear the Beef: Heat the olive oil in a large Dutch oven or heavy-bottomed casserole dish over a medium-high heat. Carefully place the beef in the pot and sear for 4-5 minutes on each side, until a deep brown crust has formed. Don't move it around too much. Once browned, remove the beef and set it aside on a plate.

Caramelise the Onions: Reduce the heat to medium-low. Add the butter to the same pot. Once melted, add all the sliced onions. Stir to coat them in the beef fat and butter. Cook slowly, stirring occasionally, for 25-30 minutes. The onions should be deeply golden, soft, and sweet. This step requires patience! Towards the end, add the minced garlic and cook for another minute until fragrant.

Build the Sauce: Sprinkle the flour over the cooked onions and stir for one minute to cook out the raw taste. Pour in the red wine to deglaze the pot, using a wooden spoon to scrape up any browned bits from the bottom. I find this is where so much of the flavour is hiding. Let the wine bubble and reduce by about half.

Braise the Roast: Pour in the beef stock and Worcestershire sauce. Add the thyme sprigs and the bay leaf. Stir everything together, then return the seared beef joint to the pot, nestling it into the onions and liquid. Bring the liquid to a gentle simmer.

Slow Cook in the Oven: Preheat your oven to 160°C (140°C fan). Cover the pot with a tight-fitting lid and transfer it to the oven. Cook for 3 to 3.5 hours, or until the beef is fork-tender and falling apart.

Prepare the Topping: About 15 minutes before the roast is done, arrange the baguette slices on a baking tray and toast under the grill for 1-2 minutes per side until lightly golden and crisp.

Melt the Cheese: Carefully remove the pot from the oven. You can either shred the beef directly in the pot or serve it whole. Arrange the toasted bread slices over the top of the beef and onions. Sprinkle the grated Gruyère cheese evenly over the bread.

Final Grill: Place the pot back in the oven, this time under a hot grill, for 3-5 minutes, or until the cheese is completely melted, bubbling, and starting to turn golden brown in spots. Keep a close eye on it to prevent it from burning. Let it rest for 10 minutes before serving.