After hulling and cleaning the strawberries, layer with an equal weight of sugar and leave 24 hours.
Drain juice into a large saucepan and bring to a fast boil, stirring frequently.
Add strawberries and boil for 20 - 30 minutes until set. (Put a little on a fridge-cold plate: it should wrinkle when pushed gently with a little finger.)
Skim.
Pour into warmed jars, making sure that each jar is full of berries; the remaining liquid can be used as strawberry jelly rather than jam, as the amount of liquid produced will exceed the amount of whole berries.
