Using a meat mallet or your rolling pin, gently pound the chicken between sheets of cling-wrap until 1cm thick.
Dip chicken in the beaten egg white and then coat in the rice flour. Shake off any excess flour.
Heat the butter and oil in a large frypan. Cook chicken until lightly browned on both sides and cooked through. Drain on absorbent kitchen paper.
Meanwhile- blend the cornstarch, brown sugar and the lemon juice in a small saucepan. Add the grated ginger, soy sauce and the stock. Bring the sauce to the boil and stir constantly until the sauce thickens.
Slice the chicken,serve drizzled with the sauce and some extra lemon wedges or slices.