First prepare the fruit juice using about 450 g fruit to obtain 150 ml of juice. Put the strawberries into a wide stainless steel saucepan, use a potato masher to crush about three-quarters of the berries, leave the rest intact in the juice. Bring to the boil and cook the crushed strawberries in the juice for about 2–3 minutes. Heat the sugar in a moderate oven (160°C/325°F/Gas 3) and add to the fruit; stir over a gentle heat until the sugar is completely dissolved. Increase the heat and boil for about 10–15 minutes, stirring frequently, until it reaches a set, skim. Pot immediately into hot sterilized jars, cover and store in a cool dry cupboard.