In a large mixing bowl, combine the mascarpone cheese, heavy cream, powdered sugar, and vanilla extract. Whip until soft peaks form.
In a separate bowl, mix the cooled espresso and coffee liqueur (if using).
Gradually fold the espresso mixture into the mascarpone mixture until well combined.
Add the chocolate cookie crumbs to the mixture and stir until fully incorporated.
Refrigerate the mixture for about 1 hour to firm up.
Once chilled, use a small cookie scoop or your hands to form the mixture into bite-sized balls.
Roll each truffle in melted chocolate, then dust with cocoa powder.
Place the truffles on a parchment-lined baking sheet and refrigerate for an additional 30 minutes to set.