250g jam setting sugar
2 tsp whiskey
Using a vegetable peeler, thinly pare the rind from one of the oranges and the grapefruit. Cut this rind into very thin strips and place into a heavy based pot.
Using a sharp knife, remove the skin and white pith from each of the oranges and grapefruit. Remove any pips and then blend the remaining fruit to a pulp. Now you equal the amount of fruit pulp with sugar. So, 250 ml fruit pulp - 250g caster sugar.
Place all the ingredients including the whiskey into pot along with the rind and gently heat until the sugar has dissolved.
Bring the mixture to the boil and then lower the heat and continue to cook on low for a further 20 minutes or until its thick. If you have a temperature probe, I took mine to 110 degrees.
You can place a plate into the freezer for 10 minutes, before testing a tbsp of marmalade to test setting.
Carefully pour the mixture into sterilized jars and lids