Peel 2 oranges and grapefruits so thickly that the white skin is completely removed. Cut the flesh into slices. Peel kiwis and cut them into thin slices. Wash and halve the grapes and possibly remove the seeds.
Arrange the fruit on 4 plates. Squeeze the rest of the orange. Mix the juice with liqueur and 1 tablespoon of sugar. Spread the marinade over the fruit and leave to stand. Coarsely chop the nuts. Caramelise 4 tablespoons of sugar in a pot.
Stir in nuts and fat. Spread the brittle on an oiled plate and let it cool down. Crumble the walnut brittle. Whip the cream until semi-stiff, allowing the vanillin sugar to trickle in. Spread the cream and nut brittle on the fruits.