Preheat the oven to 180°C. Line a baking sheet with parchment paper or a nonstick baking mat. Coarsely chop the pistachios by hand or using a chopper. Process them into fine crumbs, reserving one tablespoon for topping.
In a large mixing bowl, beat sugar and egg until light and fluffy for about 1 minute. Add butter and vanilla, mixing until well combined.
Gradually mix in flour, salt, and baking powder until just combined. Add chocolate chips and most of the chopped pistachios, folding them together with a spatula.
Scoop dough into even balls and place on the prepared baking sheet. Sprinkle tops with reserved pistachios and extra chocolate chips if desired.
Bake in the center of the oven for 12-15 minutes, until the edges are just golden. Cool on the baking sheet for 5 minutes before transferring to a wire rack.