For the strawberry-pineapple jam, chop the strawberries and pineapple and puree coarsely. Bring the mixture to the boil with the lemon juice and the preserving sugar and boil for about 4 minutes until bubbling.
Then stir in the Cointreau and immediately fill the hot jam into sterile preserving jars.
Turn the jam jars upside down for about 5 minutes, then invert again and let cool.