1) Pan fry the chicken breast in a little oil and remove from heat, cut chicken into small pieces and set aside. 2) Peel and finely chop onion. Remove seeds from green pepper and finely chop. 3) Heat the butter in a casserole and gently fry the onion and pepper until onion is transparent. 4) Stir in flour with a wooden spoon, then cold milk. Remove from the heat then gradually add the warm milk. Bring to the boil. Season with salt, pepper and nutmeg. 5) Reduce heat and simmer gently for 15 minutes. 6) Add chicken and sherry and cook for 15 minutes or until chicken is well heated through. Stir frequently to prevent sticking.