Pour the cooled coffee or espresso into a shallow dish and set it aside. In a medium mixing bowl, beat together the mascarpone cheese, confectioners’ sugar, vanilla extract, and coffee liqueur if using. In a separate bowl, whip the heavy cream using an electric mixer until stiff peaks form. Gently fold the whipped cream into the mascarpone mixture until smooth and fully combined. Quickly dip each ladyfinger into the espresso and cut them in half. Arrange two halves, stacked and crisscrossed, in the bottom of each jar. Fill the rest of the jar with the mascarpone mixture, using either a spoon or a piping bag for easier layering. Store the mini tiramisu jars in the refrigerator for 2 to 3 days, or freeze for up to one month. Just before serving, dust the tops with unsweetened cocoa powder using a tea strainer.