Melt the butter and let it cool down. Chop the rusks in the universal chopper (not too fine). Mix butter and crumbs. Spread the bottom of a springform pan thinly with oil. Put butter crumbs into the form and press them firmly at the bottom.
Place the form in a cool place. Halve melons, remove seeds and cut out balls of different sizes. Soak gelatine in cold water. Mix egg liqueur, cream cheese, sugar and sour cream. Melt the squeezed-out gelatine in a small pot. Stir in 4 tablespoons of cream, then stir into the rest of the cream. Chill the cream for 10-15 minutes until it starts to gel. Whip the cream until stiff. Fold the cream first, then 2/3 of the melon balls into the cream. Pour the cream into the mould and chill for 3-4 hours.
Chill the cream for 10-15 minutes until it starts to gel. Whip the cream until stiff. Fold the cream first, then 2/3 of the melon balls into the cream. Pour the cream into the mould and chill for 3-4 hours. Grind the pistachios finely in the universal chopper. Remove the cake from the pan and sprinkle the edge with pistachios, up to 1 tsp. Decorate cake with remaining melon balls and pistachios
waiting time approx. 4 hours