1. Shell and devein shrimp. Mince ginger root and scallion; then add to shrimp, along with sherry. Let stand 10 minutes, turning occasionally.
2. Meanwhile cut each bean curd cake first in half, then in 4 slices. Blend cornstarch and cold stock to a paste.
3. Heat oil. Add bean curd; stir-fry gently until lightly browned. Remove from pan.
4. Heat remaining oil. Add shrimp and stir-fry until pinkish. Sprinkle with soy sauce, sugar and salt; stir-fry 1/2 minute more to blend.
5. Stir in cornstarch paste to thicken. Then return bean curd and stir in gently to reheat.