Orange ice cream

Instructions

• Finely grate the zest of the oranges and the lemon, and put in a bowl.
  Add the juice of 2 oranges, and leave to steep while preparing the
  other ingredients.
• Squeeze the juice of the remaining oranges, combine with the sugar and
  cook to reduce to a thick syrup.
• Whip the cream to soft peaks. Stir the steeped juice and zest into the
  syrup. Add the juice of the lemon, then stir the syrup into the cream,
  which will immediately thicken. Add the Grand Marnier.
• Freeze in a shallow container, stirring every 30 minutes for 4 hours, then
  leave overnight to freeze before serving.