Mix cookies with butter. Cover a detachable round form with a diameter of 20 cm with cling film. Tamp the dough along the bottom of the form. Refrigerate.
Place the filling on the dough and flatten on top. Chill the chocolate cheesecake in the refrigerator for 1 hour or leave overnight.
Sprinkle cocoa on top.
Filling. Whisk the mascarpone, cream, and powdered sugar. Add cognac and chocolate melted in a water bath, beat.