Combine all-purpose flour, sugar, and a pinch of salt in a large mixing bowl. Cut in the cold, cubed unsalted butter using a pastry cutter until the mixture resembles coarse crumbs. Add the large egg and mix until the dough forms. Chill the dough in the refrigerator for 30 minutes.

Preheat your oven to 350°F (175°C). On a lightly floured surface, roll out the chilled dough to about 1/8 inch thick. Cut rounds and press them into mini tart pans, covering the bottoms and sides. Prick with a fork and bake for 20 minutes until lightly golden. Let them cool completely.

In a food processor, grind unshelled raw pistachios into a fine powder. In a saucepan, combine milk, heavy cream, sugar, and cornstarch over medium heat, whisking until thickened. Stir in the ground pistachios and vanilla extract, then remove from heat and let cool slightly.

Once the tart shells are cool and the pistachio cream has thickened, spoon the filling into each tart shell and chill in the refrigerator for at least 1 hour to set.

Before serving, remove from the fridge and garnish with extra crushed pistachios. Best enjoyed slightly chilled.