Soak gelatine in cold water. Beat the egg yolks, sugar and vanillin sugar until frothy. Squeeze the gelatine, dissolve in a small pot at low heat. Add white wine and cognac.
Whisk under the egg foam with a whisk. Place the egg mixture in the fridge until it begins to gel. Whip the cream until stiff. Beat the egg whites until very stiff. Fold in 2/3 of the cream (fill remaining cream into a piping bag with star-shaped spout) and the beaten egg white.
Halve melons, remove seeds and use a ball cutter to remove balls from the flesh. Dice the rest of the flesh. Put melon balls, except 8 for decoration, and dice in a bowl.
Fill with cream and smooth it down. Spray cream dab onto the cream. Decorate with melon balls and leave to cool slightly.