1. Position a broiler rack 6in (15cm) from the source of heat and preheat the broiler. Segment the grapefruit and oranges. Divide the citrus segments among 4 individual flameproof serving dishes.

2. Beat the egg and egg yolks together in a heatproof bowl until just beginning to foam. Beat in the Marsala and sugar.

3. Place the bowl over a saucepan of simmering water. Beat with an electric mixer for about 4 minutes, or until the zabaglione is very thick, fluffy, and warm. Spoon over the fruit. Grill for about 1 minute, or until the topping is golden. Serve immediately.

Variation:

Add 6 oz (168g) fresh raspberries or blueberries to the citrus.