Wash the fresh strawberries, removing the green stem and dry them. If the strawberries are large, I suggest to cut them in half.
Put the strawberries and lemon juice into a large pan. Heat for some minutes to soften, adding the sugar slowly. Stir over a low heat until the sugar has dissolved.
Once the liquid is clear, boil steadily for about 5 minutes, or until the jam changes from liquid to semi-liquid.
Cool for around 10 minutes.
Spoon into sterilised jars, and seal with wax paper and a lid.
Notes
To sterilise jars, simply wash in the dishwasher and pot the jam while they are still warm. Sterilise the lids by adding to a large pot of boiling water for 10 minutes. Allow to air dry.