In a large mixing bowl, combine mascarpone cheese, powdered sugar, and brewed coffee.
In another bowl, whip the heavy cream until stiff peaks form.
Gently fold the whipped cream into the mascarpone mixture until combined.
Mix in the crushed ladyfinger cookies and coffee liqueur (if using).
Cover the mixture and refrigerate for at least 2 hours, or until firm.
Once firm, scoop out portions of the mixture and roll them into balls.
Melt the dark chocolate in a microwave-safe bowl or over a double boiler.
Dip each truffle into the melted chocolate and place them on parchment paper.
Once the chocolate has set, dust the truffles with cocoa powder before serving.