This is my first foray into preserves and it was easy peasy.
You need 2lb of clementines (or you could use a mix of clementines and tangerines) which you wash, remove the stalks, cut in half and remove any pips. Then blitz them in the food processor, not completely smooth, but until the shreds of skin are small enough to make the marmalade to your liking.
Put it all in a large saucepan with a pint and a half of water and the juice of two lemons. Bring to the boil, then simmer for 15 minutes.
Add 1 kg of granulated sugar, stir and bring to a rolling boil. Stir regularly, keeping at this rolling boil until it has thickened and begun to get to setting point. This took about an hour for me.
Cool a little in the pan, then stir to make sure the bits are evenly mixed through and pour into sterilised jars.