Prick the oranges all over with a toothpick, put in a large pot and cover with warm water. Cut the rind off the lemon in thin strips and add to the oranges, along with the juice of the lemon. Leave for 12 hours.
Drain the oranges and cut away their top hats. Cut them into thin slices, then cut those into quarters. Put in a large heavy-based pot, add the sugar and leave to macerate, cove