Place the strawberries, rhubarb and lemon juice in a large pan and simmer over gentle heat until the fruit has collapsed, about 15-20 minutes.

Add the sugar, pectin and butter and bring to a boil and boil rapidly for 10-20 minutes, or until the desired setting point is reached.

Let cool for 8-10 minutes, then skim.

Pour into warmed, sterilized jars and cover the tops with wax disks.

When completely cool, cover with lids, label and store in a cool place.