You’ll need the same weight of sugar to fruit for this recipe but we think it’s only worth making with 500g or more.
1kg granulated sugar
First sterilise your jars. You can either put jars and lids through the dishwasher on a hot cycle or else wash jars and lids in hot, soapy water, rinse well and dry in a pre-heated oven (130C) for around 10 minutes until dry.
Put the raspberries in a large preserving pan (or your largest saucepan) and heat gently, lightly crushing with a spoon until the juice starts to run. Add the sugar and leave to dissolve over a gentle heat. Every so often, dip a wooden spoon into the mixture and check to make sure the sugar crystals have all dissolved. Whilst the sugar is dissolving, put a small clean saucer in the fridge - you’ll need this later on to check whether the jam is set.
Once the sugar is dissolved, turn up the heat to high and bubble vigorously for approximately ten minutes. Spoon a teaspoon onto the chilled saucer and return to the fridge for a minute or two. Check to see whether a skin has formed. If you push gently with your finger, it should be sticky and syrupy not runny. If not yet set, boil for a further five minutes and test again - you might need to repeat this process several times until the jam has reached setting point.
Once you’re happy with the set, remove from the heat, carefully ladle into the sterilised jars and fasten the lids tightly.
NB Take extra care with boiling sugar.