Cut the strawberries in half and place in a large glass bowl. Pour the lemon juice over them, cover and leave them to sit for a couple of hours.
When ready, pour the strawberries into a large saucepan over a meadium heat. Add the sugar and stir to help it dissolve. Don’t allow it to burn.
Once the sugar has dissolved, turn up the heat slightly and bring to the boil for four minutes.
Remove from the heat and add the butter.
Leave to cool for 15 minutes.
Give it another stir before pouring into jam jars.
It should keep for at least 4 months in a dark, dry cupboard.