To test the jam, place a small plate in the freezer. Combine the strawberry and apple chunks in a saucepan. Stir in the sugar until the sugar dissolves. Bring the mixture to a boil.
Add the elderflower cordial. Boil the mixture for about 10-15 minutes, or until it looks thickened and tacky. The mixture should reach 105C if using a thermometer.
You can also test the jam by placing a small amount on a frozen plate.
Leave it there for at least one minute to see if it is ready. Now If the jam forms a skin and wrinkles when pushed, it is done.
Boil the jam for another few minutes to ensure it doesn’t wrinkle. Add the lemon juice. The foamy bits from the jam should be removed and the fruit mashed gently. Divide the jam evenly into sterilized jars. Let it cool, then you can enjoy the jam.