Make the lemon cream: Grate the lemon zest and let it infuse in the lemon juice for 20 minutes. Beat the egg yolks with the sugar.

Strain the lemon juice and add it to the yolks. Cook for 5 minutes, then remove from heat and stir in the butter.

Let the lemon cream cool in the refrigerator for 30 minutes, covered with plastic wrap.

Prepare the limoncello syrup: Boil the water with the sugar and lemon zest for 1 minute. Let cool, then add the limoncello.

In a bowl, combine the mascarpone with the lemon cream and the whipped heavy cream.

Spread a layer of cream in a baking dish. Dip the ladyfingers in the syrup and arrange them over the cream. Add another layer of cream and sprinkle with chopped pistachios.

Add another layer of ladyfingers, more cream, and finish with pistachios.

Refrigerate for at least two hours before serving.