Add your room temperature or softened butter to a mixing bowl or bowl of a stand mixer.
Add in the brown sugar and white sugar and beat for about 30 seconds to combine.
Add in the egg and egg yolk (so it's one whole egg PLUS an additional egg yolk) and vanilla bean paste. Beat to combine.
Add in the flour - making sure to spoon and level, don't scoop right from the bag - baking powder, baking soda and salt.
Beat until well combined.
Fold in the chopped pistachios and chocolate.
Scoop into 1 1/2 tablespoon balls (I like the medium of these cookie scoops) and place on a baking sheet lined with parchment paper. I like to press on a few extra chocolate chips/chunks and pistachios on top. Set in the fridge for 1 hour.
Toward the end of the hour, preheat the oven to 350 Fahrenheit.
Leave only 6 of the dough balls on the baking sheet and add the other 6 to another baking sheet. You want enough room for spreading!
Bake for 11-14 minutes or until the edges are just slightly golden brown and the center looks mostly set. They will continue to firm up as they cool.
Use a round cookie cutter to swivel around the edges for perfect circles, then let cool. Top with flaky salt and enjoy!