Cut across the middle of the sponge cake to form two disks, about 1"-1-1/2" thick, each.
Blend the coffee or espresso and liqueur together. Sprinkle the bottom half of the cake with the coffee liqueur blend, enough to flavor it strongly, but don't saturate the cake so much that it will collapse.
Mix the cream cheese or mascarpone with the sugar and beat until the sugar is completely dissolved and the mixture is light and spreadable. Spread the bottom half off the cake with half of the mixture, in a fairly thick layer.
Set the second half of the cake on the bottom half and repeat the process - sprinkle the coffee/liqueur blend and spread with the remaining mixture.
Put the cocoa powder into a wire strainer and coat the top layer completely with cocoa. Refrigerate the cake for at least two hours before cutting and serving.