Braised Short Ribs with Root Vegetables

Name: Braised Short Ribs with Root Vegetables
Ingredients: 5 to 5 1/2 pounds bone-in beef short ribs; Kosher salt and freshly ground pepper; 1/4 cup vegetable oil; 2 large onions, very thinly sliced; 4 cloves garlic, minced; 2 tablespoons tomato paste; 2 tablespoons all-purpose flour; 6 cups low-sodium chicken broth; 1 8-ounce can tomato sauce; 8 thyme sprigs; 4 fresh bay leaves; 1 2-inch piece fresh horseradish, peeled and sliced, plus 1 cup finely grated, for serving; 1 tablespoon whole black peppercorns; 12 ounces carrots (4 to 6), peeled and cut into chunks; 12 ounces parsnips (4 to 6), peeled and cut into chunks; 12 ounces turnips (1 to 2), peeled and cut into chunks; 3 tablespoons chopped fresh parsley