Carefully slice each dessert shell horizontally into two even layers.
Place the bottom half of each dessert shell on an individual serving plate or in a shallow dessert dish.
Lightly brush each cake layer with the chocolate-Kahlúa soak. The cake should be moist and flavorful but not completely saturated.
Spoon or pipe a generous layer of pumpkin chocolate mascarpone filling over each bottom cake layer.
Place the remaining cake layer on top, then lightly brush it with more of the chocolate-Kahlúa soak.
Finish each tiramisu with another generous layer of pumpkin chocolate mascarpone filling.
Cover and refrigerate for at least 2 hours, or up to overnight, so the filling can set and the flavors have time to meld.
Just before serving, dust the tops generously with unsweetened cocoa powder and finish with dark chocolate shavings.