Turn up the heat. Once the jam reaches a foaming fast boil (this will read 105C on a preserving thermometer), set a timer for 10 mins. After 10 mins, put 1 tsp of the jam onto one of the frozen saucers, put into the fridge for 1 min, then push your finger through the jam. If the jam wrinkles, it is ready. If not, boil for another 2 mins and test again. As soon as the jam is ready, remove from the heat. Leave to cool for 30 mins, skim away any scum, then stir in the Pimm’s. Ladle into sterilised jars. Will keep in a cool, dark place for up to 1 year.