Preheat oven to 425°F, line baking sheets.
Boil water, butter, salt; stir in flour.
Cook dough briefly, cool slightly.
Beat in eggs one at a time, mix pistachios.
Pipe rounds, bake at 425°F then 375°F until golden.
Heat milk; whisk yolks, sugar, cornstarch.
Temper eggs with milk, cook until thick.
Stir in pistachio paste, butter, vanilla. Chill.
Whip cream with powdered sugar.
Cut puffs, fill with pistachio cream and whipped cream.
Replace tops, dust sugar, garnish pistachios.