Mix prawns, vegetable stock, sake, cornflour and salt in a food processor and process until smooth. Transfer the mixture into a small bowl. Heat sufficient oil in a wok.
Grease a tablespoon and scoop two tablespoons of the prawn mixture and shape into a ball. Gently lower the ball into the hot oil and deep-fry till lightly browned. Drain and place on a wire rack.
Repeat this process till all the mixture is used up. Mix salt and black pepper powder in a small plate. Serve the fried prawn balls hot, garnished with lemon wedges and pepper salt.