Preheat your oven to 325°F/165°C.

Season the beef chuck roast generously with salt and pepper.

In a large oven-safe pot or Dutch Oven, heat the oil over medium-high heat.

Sear the roast beef on all sides until browned. Add the red wine to the pot. Let it simmer and reduce by half. Add the mushroom, onion, and garlic to the pan and add the beef broth. Season with salt and pepper, cover and place in the preheated oven for 3-4 hours or until beef is tender and easily shredded.

Once the beef is done, remove it from the pot and set aside to rest.

Strain the cooking liquid to remove the solids (optional), then measure out 2 cups of broth. Return the broth to the pot and place over medium heat. In a small bowl combine the cornstarch and water to create a slurry.Gradually whisk the slurry into the simmering broth.Continue to cook, whisking constantly, until the gravy thickens. Season with Salt and Pepper to taste.

Shred the cooked beef or cut into slices.

Toast the sliced of white bread. Place a slice of toasted bread on each plate. Add a scoop of mashed potatoes on each piece. Top with a generous amount of sliced roast beef. Pour the rich gravy over the entire dish.

In a large pot, bring the peeled and cubed potatoes to a boil in salted water.

Cook until the potatoes are tender, about 15-20 minutes.

Drain the potatoes and return them to the pot.

Add the milk and butter, then mash until smooth and creamy.

Season with salt and pepper to taste.