Step 1
Preheat oven to 140°C. Place the beef and flour in a large bowl. Season. Toss the beef to coat.
Step 2
Heat the oil in a large flameproof roasting pan over high heat. Add the beef and cook for 2 mins each side or until the beef is golden brown. Transfer the beef to a plate.
Step 3
Add the onion, combined mushroom and garlic to the pan and cook, stirring, for 5 mins or until the onion softens. Return the beef to the pan with the wine or apple juice, stock, thyme and bay leaves. Bring to a simmer. Remove from heat.
Step 4
Cover the pan loosely with foil. Roast, turning the beef occasionally, for 2 hours or until the beef is falling off the bone and the sauce thickens slightly. Set aside, covered, for 5 mins to rest.
Step 5
Meanwhile, to make the polenta, combine the stock and milk in a large saucepan. Bring to the boil over medium-high heat. Reduce heat to medium-low. Gradually add the polenta in a thin, steady stream, whisking constantly. Cook, stirring with a wooden spoon, for 10 mins or until the polenta thickens. Remove from heat. Add parmesan and mascarpone and stir to combine. Season.
Step 6
Divide the polenta among serving bowls. Top with beef and spoon over the sauce. Serve with baby broccoli.