To make the massaman paste: Process all the ingredients in a liquidiser or food processor. If it's too dry, add a little water to make a paste. Use in this recipe, store any remainder in the refrigerator for upto 3 weeks.
Heat the oil in a large saucepan and brown steak in batches. Remove from pan.
Add the potatoes and onion to same saucepan and stir until lightly browned. Add 5 tablespoons curry paste and stir over high heat for 1 minute.
Add the coconut cream, steak, water and sugar. Bring to the boil, then simmer for about 45 minutes, uncovered or until the meat is tender.