Simmer mandarins with water in a pot uncovered for 45 mins. Enough water to cover the mandarins.

Drain and discard the water and let it cool enough to handle.

Break mandarin into pieces and remove piths.

Put mandarin in food processor and blitz til skin is in small chunks (think what size you would spread on toast).

Put blitzed mandarin into a pot and add the sugar.

Cook on high heat until boiling and then reduce to lowest simmer. Stir constantly.

Continue simmering until jam texture is ready. To test, take spoon a small amount into a little dish, put it into the freezer for 5mins and then check if it's jam texture.