In a food processor or mixing bowl, whip the mascarpone cheese and confectioners' sugar until smooth and creamy. Beat in the espresso. The mixture should be creamy and easy to spread at this point; if not, add a bit more espresso. Spread a thick layer of tiramisu filling over a baked pizza shell. Dust the cheese liberally with cocoa powder, followed by a very light dusting of confectioners' sugar to achieve a dappled effect. Fresh fruit such as raspberries can be arranged around the edge of the pizza as a garnish.