- Mix butter, powdered sugar, egg yolk and egg liqueur until foamy (approx. 20 minutes so that the cream becomes nice and loose).
- Mix the rum and coffee.
- Place the first layer of sponge fingers in a springform pan, drizzle with the rum and coffee mixture, pour the cream on top, drizzle with the sponge fingers again and finish with the cream.
- Whip the cream with the vanilla sugar and whipped cream until stiff and garnish the cake with whipped cream.