1 Peel one orange, very thinly, taking care not to remove any pith.
2 Cut the peel into very fine strips and retain.
3 Peel the remaining oranges, removing all the pith, and remove the pith from the first orange.
4 Slice the oranges, removing any pips (seeds).
5 Arrange the slices in a 30 x 20 x 5cm/ 12x8x2 inch ovenproof glass dish. Spoon the liqueur over the slices, and add the orange peel.
6 Place the sugar and water in a 1 litre/1 3/4 pint (4 1/2 cup) jug and microwave on full power for 10-13 minutes, until a dark golden caramel results.
7 Pour the caramel over the oranges.
8 Cool the oranges, then chill overnight in the refrigerator. Serve with yogurt or whipped cream.