In a large mixing bowl, whip the heavy cream until soft peaks form. Gradually add the powdered sugar and continue whipping until stiff peaks form.
Gently fold in the mascarpone cheese and vanilla extract until well combined and smooth.
In a shallow dish, combine the brewed espresso and coffee liqueur, if using.
Quickly dip each ladyfinger into the espresso mixture, ensuring they are soaked but not soggy.
In a 9x9-inch baking dish, layer half of the soaked ladyfingers on the bottom.
Spread half of the mascarpone mixture over the ladyfingers, smoothing it out evenly.
Sprinkle half of the crushed pistachios over the mascarpone layer.
Repeat the layers with the remaining ladyfingers, mascarpone mixture, and crushed pistachios.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight for best results.
Before serving, dust the top with cocoa powder and garnish with additional crushed pistachios if desired.