Heat oil in a skillet, add chicken pieces and brown them evenly all over. Pour beer in a medium size saucepan and bring to a boil over medium heat. Add browned chicken, cover saucepan and cook over low heat for 15 minutes. Season with salt and pepper. Add lemon juice and Pisco or Scotch. Cover saucepan again and continue cooking until chicken is tender. Add onions, hot red ají and cook until they are soft.
Remove chicken pieces from the saucepan and set aside, covered. Dilute 2 tablespoons cornstarch in water and stir into boiling sauce. Cook, stirring, for approximately 3 minutes. Serve chicken pieces with this sauce and white cooked rice.