Brown chicken in shortening over low heat; transfer to a covered roasting pan. Sprinkle chicken with salt and pepper. Add water; cover and bake at 350° for 50 minutes or until chicken is tender. Remove chicken to a heated serving platter; reserving pan liquid.
Combine melted butter and flour, stirring until a smooth paste is formed. Heat reserved pan liquid in a small saucepan over medium heat. Add flour mixture, stirring until well blended. Cook over medium heat 1 minute, stirring constantly. Add mushrooms; stir well. Pour sauce over chicken; serve hot.