Beef Bourguignon

Name: Beef Bourguignon
Ingredients: 2 1/2 pounds round roast, cut into 1-inch cubes; Kosher salt and freshly ground black pepper; 1/4 cup all-purpose flour; 1 tablespoon olive oil; 8 ounces slab bacon, diced; 4 large carrots, cut on the diagonal into 1-inch pieces; 2 medium yellow onions, sliced; 1 stalk celery, cut into 1-inch pieces; 2 cloves garlic, thinly sliced; 2 bay leaves; 2 tablespoons tomato paste; 1 pound frozen pearl onions; 1 teaspoon fresh thyme; One 750-milliliter bottle dry red wine; 2 tablespoons unsalted butter, at room temperature; 10 ounces white mushrooms, quartered; Mashed potatoes, for serving