Bake 12 unfilled tart shells in an oven according to directions on package.
In a medium bowl combine Mascarpone, coffee liqueur and brown sugar; stir until combined and set aside or refrigerate until ready to use. Spoon teaspoonfuls of melted chocolate into the bottom of each baked tart shell. Top with spoonfuls of Mascarpone mixture. Sift cocoa over each just before serving.