Put the chopped marrow, onions and apples into a large preserving pan, add the rest of the ingredients and the bag of spices and stir together, then place over a medium heat. Bring to a simmer, then reduce the heat and simmer gently from 1 ½-2 hours or until well blended and thick.
Take the pan off the heat, cool and remove the muslin, squeezing the liquid form from the bag. Spoon it into sterilised jars with vinegar-proof lids, filling them to within 1cm of the top.
Ensure the rims are clean, screw on the sterilised lids and store in a cool place for up to 12 months. Once open, store in the fridge and use within 1 month.
