In a large bowl combine the chicken, sherry, soy sauce and 1/2 teaspoon salt. Mix together, cover and refrigerate. Let marinate for 15 to 20 minutes.
In a small bowl, beat together the eggs, 1/4 cup cornstarch and baking powder to form a batter. In a wok, heat 2 cups oil to 350 degrees F (175 degrees C). Coat chicken with batter and fry in wok until browned. Cut into bite size pieces and set aside.
In a medium bowl combine the sugar, 1 tablespoon cornstarch, broth, lemon juice and 1 teaspoon salt. Mix together and add lemon slices. Heat 2 tablespoons oil in wok and slowly stir in lemon sauce mixture. Cook, stirring, until sauce is clear. Pour sauce over chicken and serve.