Fluffy and Irresistible Tiramisu Frosting. This tiramisu frosting could dress up even the most drab of cupcakes. It’s a Swiss meringue buttercream frosting recipe, which means that it’s silky smooth and not overly sweet. However, this tiramisu frosting trades some of the butter for mascarpone cheese and is finished with rum, espresso, vanilla, and a dusting of cocoa powder.