Pour the cooled espresso and optional coffee liqueur into a shallow dish and stir briefly to combine.

In a large mixing bowl, beat the softened mascarpone, pistachio cream, sifted powdered sugar, and vanilla extract with a hand mixer on medium speed until smooth and uniform.

In a separate chilled bowl, whip the heavy cream on medium-high speed until medium-stiff peaks form, then gently fold it into the pistachio-mascarpone base using a spatula until fully incorporated.

Quickly dip three ladyfinger halves per cup into the espresso mixture for 1 to 2 seconds per side, then arrange them in the bottom of 4 individual serving cups or glasses.

Spoon or pipe half of the pistachio mascarpone cream evenly over the soaked ladyfingers in each cup.

Dip the remaining ladyfinger pieces in espresso and create a second layer in each cup, then top with the remaining pistachio cream and smooth the surface.

Cover the cups and refrigerate for at least 2 hours, or ideally overnight, before dusting with cocoa powder and topping with chopped pistachios just before serving.