Create a double boiler by placing a heatproof bowl over a pot of simmering water (the bowl shouldn't touch the water).

Add egg yolks and sugar to the bowl. Whisk constantly for 5-7 minutes until the mixture is thick, pale, and reaches 160°F (71°C) on a thermometer. This pasteurizes the eggs.

Remove from heat and let cool to room temperature, whisking occasionally (about 15 minutes).

In a separate large bowl, beat the mascarpone cheese with pistachio paste, vanilla, and salt until smooth and creamy. Don't overbeat or it may become grainy.

Gently fold the cooled egg mixture into the mascarpone until fully combined.

In another bowl, whip the heavy cream to stiff peaks. Gently fold the whipped cream into the mascarpone mixture in three additions until no streaks remain. Set aside.

Combine the cooled espresso, liqueur (if using), and sugar in a shallow dish. Stir until sugar dissolves.

Quickly dip each ladyfinger into the coffee mixture for about 1-2 seconds per side—they should be moistened but not soggy.

Arrange a single layer of dipped ladyfingers in the bottom of a 9x13-inch dish (or an 8x8-inch dish for thicker layers).

Spread half of the mascarpone cream evenly over the ladyfinger layer.

Sprinkle half of the chopped pistachios over the cream layer.

Repeat with another layer of dipped ladyfingers, the remaining mascarpone cream, and smooth the top.

Cover tightly with plastic wrap and refrigerate for at least 4 hours, preferably overnight, to allow the flavors to meld and the texture to set.

Just before serving, dust the top generously with pistachio powder or finely ground pistachios.

Sprinkle with the remaining chopped pistachios and add a few whole pistachios for visual appeal.

Slice into squares and serve chilled.