If the strawberries are large, cut them in half. Put the strawberries and lemon juice into a large pan. Heat for a few minutes to soften, add the sugar and stir over a low heat until the sugar has dissolved.
Once the sugar has dissolved and the liquid is clear, boil steadily for about six minutes, or until at setting point. To test if the jam is at setting point, spoon a little onto a cold plate, leave for a minute and then push the jam with your finger. If the jam crinkles and separates without flooding back, setting point has been reached.
Set aside to cool a little. Spoon into sterilised jars, label and seal with wax paper and a lid.