01 - Pulse pistachios in a food processor until finely ground. Add flour, powdered sugar, and salt; pulse to combine. Add cold butter and pulse until coarse crumbs form. Add egg yolk and pulse a few times. Drizzle in ice water, 1 tablespoon at a time, pulsing just until dough begins to clump.
02 - Press dough evenly into the bottom and sides of a 9-inch tart pan with removable bottom. Chill for 20 minutes.
03 - Preheat oven to 350°F.
04 - Line crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes. Remove weights and bake 8 more minutes, until golden. Cool slightly.
05 - In a mixing bowl, whisk eggs and sugar until smooth. Whisk in orange zest, juice, cardamom, heavy cream, melted butter, and salt until fully blended.
06 - Pour filling into the slightly cooled crust. Bake at 325°F for 20–22 minutes or until filling is just set but still slightly wobbly in the center.
07 - Cool tart at room temperature, then chill at least 1 hour before serving. Garnish with chopped pistachios and orange zest or candied orange.