Preheat oven to 300 degrees F.
In a food processor, whip the mascarpone cheese and confectioners' sugar until smooth and creamy. Add espresso, process until mixture is creamy and spreadable. Add a bit more espresso if mixture is too stiff.
Spread the tiramisu filling over baked pizza shell. Create a dappled effect by first dusting the cheese liberally with cocoa powder, followed by a very light dusting.
Place on a baking sheet in the oven just until slightly warmed.
Recipe courtesy of Rick Nielsen and Bill Jacobs, Piece Brewery and Pizzeria, Chicago, IL