Nectarines naturally contain pectin (as do plums) and that is the stuff that helps give it the jammy texture - so that means that all you need for nectarine jam is sugar, nectarines and some lemon juice. And a saucepan!
Nectrarines - chopped, stones removed, no need to peel
Sugar - half the weight that you have of nectarines. I used caster sugar
Water - I used 1 cup of water - to about 8 nectarines
Lemon juice - I used the juice of half a lemon, something like that will be fine.
Put all the ingredients in a pan, stir and bring to a rolling boil, stir frequently and boil for about 30 minutes - or until thick and jammy. Then leave to cool. Pour into a jar, jug, whatever you fancy. My 8 nectarines made one average jam sized jar. In a sterilised jar (boil it for 5 minutes) the jam will keep in the fridge for 6 months!
The jam is thick and a beautiful colour. It's really tasty too!