Quickly dip ladyfingers into the coffee mixture (just a second per side—any longer and they’ll fall apart). In a 9x9 inch pan, layer dipped ladyfingers in a single layer.
Spread half of the mascarpone-pistachio mixture over the ladyfingers.
Drizzle with some of the reserved pistachio cream.
Repeat: layer ladyfingers, spread the remaining mascarpone-pistachio cream, and finish with a final drizzy of pistachio cream.
Top with finely chopped pistachios. (If you are making this to eat the next day, refrain from this step top with chopped pistachios before serving the day of).
Cover and refrigerate for at least 4 hours (or overnight).