Horseradish Sauce. Place short ribs on serving platter and keep warm. Skim fat from cooking liquid. Combine flour with 1 /2 cup water, mixing until smooth; combine with cooking liquid, bring to a boil, stirring constantly, reduce heat and cook slowly 3 minutes. Strain, if necessary, and serve with short ribs. Garnish platter with tomato wedges and parsley. Serve Horseradish sauce with short ribs. HORSERADISH SAUCE: Combine sour cream, horseradish, mustard and salt in small bowl. Cover and refrigerate.