If you dont have fruit , Marrow or Courgette jam is scrumptious.
Just peel and dice marrow or courgettes inc seeds if they are small, weigh and weigh out same amount of sugar, just normal sugar as the marrow is high in pectin
put the marrow cubes in a pan and cook with a bit of water until tender then drain and mash. Take off the heat and add the sugar and add a good squeeze of lemon and a little ginger . Stir till the sugar has melted then gently boil till the jam is ready, this jam is pretty quick about 2o mins should do it. Then allow to cool for a minute or two before jarring as normal.
It tastes like barley sugar and does darken with age. Enjoy