Separate 6 eggs. Beat the egg whites until stiff with 4 tablespoons of water and 100 grams (approximately 1/3 cup) of sugar until glossy and stiff.
Mix the yolks with 4 tablespoons of warm water and 60 gram (approximately 3 tablespoons) of sugar until fluffy. Fold the egg whites into the egg yolks. Mix the flour with the baking powder and 100 grams (approximately 3/4 cup) of cornstarch. Gently fold the flour into the egg mixture. Do not over stir.
Spread the dough on a parchment-lined sheet tray and bake in an oven preheated to 180°C (approximately 350°F) for about 15-20 minutes until golden brown. Let the cake cool slightly in the pan.
Separate the two remaining eggs. Beat the egg whites until stiff. Beat the egg yolks with the remaining sugar until creamy. Bring the remaining cornstarch and milk to a boil. Slowly stream the milk into the eggs and return to the pot. Bring to a boil while stirring.
Remove from heat and stir in the liqueur. Fold in the egg whites and chill for 30 minutes.
Warm the raspberry jam and spread over the cake.
Clean the raspberries. Rinse the nectarines, cut in half, and remove the pit. Cut finely into thin strips.
Spread the cooled custard onto the cake and arrange the raspberries and nectarines decoratively on the custard.