Lingonberry or Cranberry Jam

Depending on the tartness of the berries you may need to adjust the amount of sugar.
1 lb. 2 ounces (500 g) frozen or fresh lingonberries or cranberries
A scant cup (7 oz/200g) of caster (superfine) sugar (hs note: I just gave my regular granulated sugar a whirl in the food processor for 15-20 seconds)
Finely grated rind and juice of 1 lemon
1 small apple, peeled and cored
Rinse the berries, if necessary, then drain well and put them in a non-metallic bowl with the sugar and lemon juice. Leave overnight, turning once or twice.
Coarsely grate the apple and put it into a jam-making pan or other heavy based saucepan with the grated lemon rind. Strain in all the juice from the berries (hs note: I didn't end up with a ton of juice, but scraped all the thick, sugary juice in) and add two wooden spoonfuls of berries, leaving the rest of the berries in the bowl for now. Add 1/2 cup (125 ml) water and simmer for 20-30 minutes, or until the apple is very soft and the whole lot has thickened (hs note: I ended up ~10 minutes). Add the rest of the berries and heat through for 5-8 minutes. Pour into sterilized jars. Seal tightly and turn upside down. Cover with a cloth and leave to cool completely before turning upright and storing in a cool place. The jam will keep for a couple months but, once open, keep it in the fridge and use fairly quickly.
Makes about 2 cups.