To make the crust, combine the all-purpose flour, 1/4 cup of granulated sugar, kosher salt, and cold, cubed butter in a food processor. Pulse until the mixture resembles coarse, sandy crumbs with no large lumps of butter remaining.
Add the egg yolk and ice water to the food processor and pulse just until the dough begins to clump together and form a ball. Be careful not to overmix.
Press the dough evenly into six 4-inch tart pans with removable bottoms, ensuring it goes up the sides. Use a fork to prick the bottoms all over, then freeze the crusts for 30 minutes until firm. Meanwhile, preheat your oven to 350°F (175°C).
Bake the frozen tart crusts for 15-18 minutes, or until the edges are lightly golden brown. Remove from the oven and let them cool completely on a wire rack.
For the filling, whisk together the heavy cream, whole milk, matcha powder, and 1/3 cup granulated sugar in a medium saucepan over medium heat. Heat the mixture until it is warm and the sugar has completely dissolved, but do not let it boil.
In a separate bowl, lightly beat the 2 eggs. Gradually whisk about 1/2 cup of the warm matcha mixture into the eggs to temper them, then pour the entire egg mixture back into the saucepan, whisking constantly.
Cook the custard over low heat for 3-5 minutes, stirring constantly with a spatula, until it has thickened enough to coat the back of a spoon. Remove from heat and stir in the almond extract and finely ground pistachios.
Pour the warm filling into the cooled tart shells. Garnish the tops with the roughly chopped pistachios. Refrigerate the tarts for at least 4 hours, or until the filling is completely set, before serving.