1. Place brisket on bottom half of bun; top with sliced onion.
2. Drizzle horseradish and Vidalia onion sauces over all.
3. Cover sandwich with top of bun and serve.
Nutritional information per serving: Calories 559; Total Fat 16g; Saturated Fat 3g; Tran Fat 0; Cholesterol 125mg; Sodium 787mg; Total Carbohydrate 50g; Dietary Fiber 2g; Total Sugars 4g; Protein 47g