Wash and possibly halve the grapes. Peel the orange and grapefruit so that the white skin is completely removed. Cut out fillets between the parting skins. Squeeze juice from the parting skins directly into a bowl and mix with 1 tablespoon of sugar.
Chop nuts. Wash, quarter, core and dice apple and pear. Peel and slice the banana. Mix everything with the fruit juice immediately.
For the zabaglione, mix egg yolk, rum, cinnamon and 75 g sugar with a whisk in a metal bowl.
Then whip in a hot water bath for 7-10 minutes until foamy. Remove from the water bath and continue beating until lukewarm. Spread the zabaglione over the fruit salad and serve immediately.