Melt half the butter over medium heat in a large skillet. Add the onion and saute till tender. Remove from the pan and reserve. Peel, quarter and core the apples. Melt 1 tbsp butter in skillet and brown chicken breasts on both sides. Add apples, Calvados, allspice, apple juice, salt and pepper to skillet. Cover and cook over low heat 20 minutes. Remove chicken to a platter and keep warm. Return onions to pan. Blend together remaining butter and flour. Stir into sauce and cook for 5 minutes till sauce is thickened. Pour sauce over chicken and serve immediately. Makes 4 servings.