To prepare stock place chicken or hen pieces in a large pan. Cover with water. Add carrot, celery, leek, oregano, salt, pepper, bay leaf and parsley sprig. If its a hen boil for 2 hours, a chicken will cook in less time. When cooked, remove chicken bones and cut meat in pieces. Save stock.
On a separate bowl, soak bread slices in milk combined with stock (about ½ cup). Blend or process.
Sauté onion, add garlic, blended aji and tomato in a pan. Season to taste. Add the processed bread. Stir until thickened.
Add 4 cups of chicken or hen stock and bring to a boil for 20 minutes. Add potatoes, and cheese. Boil for 10 minutes more until potatoes are cooked.
Finally add milk and chicken pieces.
Serve in soup dishes and garnish with chopped parsley.