Ghoulish Petits Fours

Using a 1 1/2-inch cookie cutter, cut out circles from cake. Brush off any crumbs with a pastry brush. Fit a pastry bag with a plastic coupler, and top cake rounds with icing in a ghost or hat shape,about 1 inch high. Place a wire rack over a rimmed baking sheet; set aside. Set an iced cake round on a fork; hold over bowl of glaze. Using a large spoon, drizzle glaze evenly over cake and icing until completely covered. Transfer to wire rack. Repeat with remaining rounds. Let set, about 5 minutes. Place chocolate in a heatproof bowl set over a pan of barely simmering water; stir chocolate until melted. Transfer to a disposable pastry bag or resealable plastic bag; snip off tip with scissors. Pipe eyes and a mouth onto ghosts.