Preparation: Rinse bean sprouts; drain. Separate layers of onion and slice into thin strips to match sprouts. Cut steak into slices across the grain 1/4" wide by 2" long. Mix stock, soy sauce and sherry in a cup. Prepare Szechuan pepper/salt: heat dry wok to medium and add Szechuan peppercorns, stirring constantly until peppercorns exude a strong aroma; remove from heat. Crush peppercorns with salt, using rolling pin or blender. Sift to remove coarse pieces. Store in closed jar. Scalding: In large bowl, cover onions with boiling water; drain in 10 minutes. Add sprouts, cover both with boiling water; drain in 3 minutes. Sprinkle with about 1/2 tsp. Szechuan pepper/salt. Stir-fry: Add oil to hot wok. When oil starts to smoke, add steak, and stir-fry briskly for 1 minute or until meat loses pinkness. Push meat aside in wok; add stock mixture and bring to boil. Dribble in thin cornstarch paste until light gravy is formed. Mix with beef. Pour over sprouts and onions in a serving bowl. Serve.