Put roast into a bowl or plastic bag; add onion, garlic, vinegar, wine, horseradish, sugar, salt, and pepper. Marinate roast overnight in refrigerator. Remove roast, reserving marinade. Drain meat on paper towels; roll in flour. In a large saucepan or Dutch oven, heat oil and brown roast on all sides. Add half of the marinade; cover and simmer 2 1/2 to 3 hours or until tender. Makes 6 servings.
To cook the roast in a slow cooker: After browning the roast on all sides, place it in the slow cooker, add half of the marinade and cook on low for 8 to 12 hours, or high for 4 to 5 hours.
Approximate Nutrient Analysis per serving:
500 calories, 17 g fat, 5 g saturated fat, 175 mg cholesterol, 550 mg sodium, 13 g carbohydrate, less than 1 g fiber, 4 g sugar, 60 g protein