Crumble the ladyfingers. Chop the chocolate and melt with the butter over a hot water bath. Remove from heat, cool slightly, mix with the crumbled ladyfingers and pour into a springform pan lined with parchment paper or plastic wrap. Spread evenly, press firmly into the bottom of the pan and refrigerate.
Soak the gelatin in cold water. Rinse the berries, hull, pat dry with paper towels and chop into pieces. Combine the cream cheese, quark, lemon juice, lemon zest and powdered sugar and stir until smooth. Heat the gelatin in a small pan with the liqueur to dissolve. Stir in 3-4 tablespoons of the cream cheese mixture and then mix with the remaining cream cheese mixture. Beat the heavy cream until stiff. Fold into the cream cheese mixture and then fold in the strawberries. Pour into the spingform pan, smooth the top and chill for at least 4 hours. Release the cheesecake from the pan and remove the plastic wrap or paper. Serve cut into slices.