300g rhubarb cut into slices
300g cooking apples, peeled, cored and chopped
600g unrefined granulated sugar (or sugar alternative)
juice of two lemons
This quantity should make approx 4 jars of a jam, so first of all wash all the jars and then place in a medium hot oven 5 to 10 mins.
Put the rhubarb and apple in a large heavy based pot, with a few tablespoons of water, bring to the boil, reduce the heat, put the lid on and allow to simmer for 25 mins.
With a masher mash any lumps. Add the sugar, turn up the temperature and cook for a further 10 minutes or so. Add the the lemon juice. When the thermometer reaches 103 degrees Celsius, take a spoonful of the jam and put it on a pre chilled plate, leave it for a few moments, then nudge it with a spoon and if it wrinkles it is ready.
Pour the jam into the sterilised jars and seal the lid tightly. The jam should keep for a few months, however once opened keep refrigerated.