Mix the quark, mascarpone, egg yolk and vanillin sugar with the whisks of the hand mixer. Place half of the lady fingers side by side with the sugared side up on the bottom of a mould (approx. 13 x 8 cm). Sprinkle with half of the espresso and liqueur. Spread half of the mascarpone cream smooth on top. Place the remaining lady fingers on top and sprinkle with the remaining espresso and liqueur.
Spread the rest of the mascarpone cream on top. Chill for about 4 hours. Dust with cocoa before serving. Decorate with lemon balm