Lightly season 2 cups water with salt and bring to a boil. Quickly whisk in the polenta until it has been fully incorporated. Reduce the heat to a low simmer. Add the butter and allow the polenta to cook uncovered for 30 minutes. Stir in the mascarpone and season to taste with salt.
This may be made in advance and kept in the refrigerator. Reheat in the microwave just before serving.
Assembly: Reheat the three components of the dish separately.
On each of 6 large plates, place a couple of spoonfuls of polenta in the center of the plate.
Carefully remove the bones from the hot ribs and place the beef short ribs over the bed of polenta.
In a pan over medium heat, bring the reserved braising liquid to a simmer. Once the sauce is hot, check for seasoning and, if needed, add a touch of salt and pepper. Spoon the sauce around the beef short ribs and polenta. Carefully place the root vegetable ragout on the beef. Serve and enjoy!