Wash the orange and rub dry. Grate the peel and squeeze the orange. Beat egg yolk and sugar until creamy. Stir in mascarpone, quark, orange peel and orange juice. Place one half of the lady fingers close together in a flat casserole dish. Sprinkle with half of the espresso and liqueur.
Spread one half of the mascarpone cream on top. Cover again with lady fingers, soak with espresso and liqueur and spread the rest of the cream on top. It is best to leave it to soak overnight in the refrigerator. Dust with cocoa. Decorate with orange slices and mint leaves if desired