Using a sharp kitchen knife, remove the white skin from the grapefruits and oranges, leaving the flesh exposed. Cut the slices of fruit from the separating skins, working over a baking dish to catch the juice. Squeeze the fruit halves with the remaining pulp and add to the collected juice form. Measure the indicated mass of juice and set aside, use the rest elsewhere.
Place egg, sugar, egg yolks, Campari, white wine and fruit juice set aside in a large enough bowl. Beat over a hot water bath until creamy. Put it on the spot in a cold water bath and stir the sabayon cooled down.
Whip the cream until stiff. Stir into the sabayon. Divide the Campari sabayon evenly into soup plates or other deep plates. Arrange the grapefruit and orange slices decoratively on top. Sprinkle with a small amount of powdered sugar and bring to the table on the spot.
Sprinkle pistachios or lightly toasted almond flakes over the dessert.