The potatoes should be yellow, waxy ones, such as Petrones or Desirees. Heat half the oil in a large heavy pot. Brown lamb well in batches and, using a slotted spoon, remove to a plate.
Add remaining oil. Add onion and cook until softened. Add parsley, garlic and capsicum. Return lamb to pot, stir and add stock and freshly ground pepper to taste. (Do not add salt yet as pecorino is a salty cheese).
Reduce heat, cover, and simmer for 30 minutes. Add potato and simmer for another 20 minutes, or until lamb is almost tender. Stir in cheese and cook for 10 minutes.
Season with freshly ground pepper and salt to taste. Best if cooked 1 to 2 days ahead and refrigerated. Like all casseroles, it will improve in flavour during the resting period.Servings: