Step 1: Prepare your pistachios. Finely grind 1 cup of shelled pistachios in a food processor until it forms a fine meal. Coarsely chop the remaining 1 cup of pistachios for garnish later.
Step 2: Prepare the coffee soak. In a shallow dish, combine the cooled strong espresso (or coffee) and the optional granulated sugar and pistachio liqueur/Amaretto. Stir until sugar is dissolved.
Step 3: Make the mascarpone cream. In a large mixing bowl, combine the softened mascarpone cheese, cold heavy cream, powdered sugar, and vanilla extract. Beat with an electric mixer on medium-high speed until the mixture is light, fluffy, and holds firm peaks. Be careful not to overbeat, as mascarpone can separate.
Step 4: Gently fold the finely ground pistachios into the mascarpone cream until just combined. Do not overmix.
Step 5: Assemble the first layer. Quickly dip each ladyfinger into the cooled coffee mixture (do not soak for too long, just a quick dip on both sides). Arrange a single layer of soaked ladyfingers at the bottom of a 9×13 inch baking dish or similar sized serving dish.
Step 6: Spread half of the pistachio mascarpone cream evenly over the first layer of ladyfingers.
Step 7: Repeat the layering process: Add a second layer of coffee-soaked ladyfingers, followed by the remaining pistachio mascarpone cream. Smooth the top with a spatula.
Step 8: Chill the tiramisu. Cover the dish tightly with plastic wrap and refrigerate for at least 6 hours, or ideally overnight, to allow the flavors to meld and the tiramisu to set properly.
Step 9: Garnish and serve. Just before serving, remove the plastic wrap and generously sprinkle the top with the coarsely chopped pistachios. You can also add a light dusting of cocoa powder or finely grated white chocolate for an extra touch. Slice and serve cold.