Pick over fruit, remove stalks and wash. Put in a pan with about half the fruit’s depth of water. Bring to the boil and simmer gently until fruit is soft and broken down, then press it through a fine sieve and weigh the pulp. Return pulp to pan with sugar, bring to the boil again and boil gently for about 1 hour, until creamy in consistency, stirring constantly to prevent burning. Pot and cover immediately in usual way.