Dark Seville Orange Marmalade

• 3lb/1.5 kg Seville oranges
• 5 pints/2.5

Wipe the fruit and cut the oranges in half. Squeeze out the juice and pips. Tie the pips into a piece of muslin to suspend in the pan. Put the juice in a pan with the water and juice of the lemon. Cut the fruit into thick shreds and add to the pan. Simmer for about 1½ hours until the peel is tender. Take out the bag of pips and squeeze out any liquid into the pan. Stir in the sugar and black tr