Beat egg in a shallow dish with salt and pepper. Mix bread crumbs with walnuts and set aside. Pound each chicken breast to 3/4" thickness. Dip into flour, then in egg mixture, then in bread crumbs with walnuts. Melt butter or margarine in large skillet. Brown the meat on both sides, turn down heat and cook for 20 minutes. Place the breasts on a platter, add diced onion to drippings in skillet and saute until glazed. Add curry powder and stir in whipping cream. Make a paste with cornstarch and lemon juice, stir into cream and bring to a boil, stirring constantly until thickened and smooth. Season with salt and pepper and a dash of sugar. Place chicken breasts in sauce and simmer gently for 5 minutes.
