Peel and core the pears and apples, then chop them coarsely into small pieces. Peel and chop the onions.
Add everything in a large, heavy-based saucepan - but retain half of the cider vinegar. Season with salt and pepper.
Bring to the boil, stirring until the sugar has melted. Then let it simmer gently for 25 minutes. Add the remaining vinegar and cook for a further 30 minutes. It is ready when you get a thick, sticky jam.
Transfer it into
sterilized jars and seal well.
Keep in a cool place or in the fridge and it will keep for some time, but use within a few days once opened.