To make the crust: Melt the butter and set aside to cool. In the bowl of your food processor add your graham crackers, pistacios and sugar. Pulse or process until the crackers and pistacios are pretty fine. Add the melted butter and pulse until all is combined and you have a moist dough. This will make 4-6 tarts or one large pie. Place enough graham cracker mixture into your pans to cover the bottom and up the sides pressing to firmly pack it. Prebake the tarts at 375 degress for 7-10 minutes. Remove from the oven when lightly browned and cool.
Using a carrot peeler, remove the zest of 3 lemons, being careful to avoid the white pith. Put the zest in a food processor fitted with the steel blade. Add the sugar and pulse until the zest is very finely minced into the sugar.
Cream the butter and beat in the sugar and lemon mixture. Add the eggs, 1 at a time, and then add the lemon juice and salt. Mix until combined.
Pour the mixture into a 2 quart saucepan and cook over low heat until thickened (about 10 minutes), stirring constantly. The lemon curd will thicken at about 170 degrees F, or just below simmer. Remove from the heat and cool or refrigerate.
After you have completely chilled the lemon curd in the refrigerator, add to each tart pan. Store back in the refrigerator until ready to serve. Serve with a dollop of whipped cream and berries of your choice.