In the bowl of a slow cooker, combine the onions, garlic, carrots, parsnips, mushrooms, tomatoes, and sage. Season the short ribs with 1 1/2 teaspoons salt and 3/4 teaspoon pepper and nestle them among the vegetables. Add the wine. Set the slow cooker to high and cook until the meat is tender and falls from the bones, 8-9 hours. Using a large spoon, skim off the excess fat and discard. Divide the ribs and vegetables among individual bowls and spoon the sauce over the top. Serve with the crusty bread.
If You Don't Have a Slow Cooker: Heat oven to 300° F. Follow the recipe above using a Dutch oven or large casserole. Bake, covered, until the meat is tender and falls from the bones, 4 hours.