Preheat the oven to 350°F (175°C).

Cream the unsalted butter with dark brown sugar and granulated sugar in a mixing bowl until light and fluffy.

Add the large egg and vanilla extract, and mix well.

Whisk together the all-purpose flour, baking powder, kosher salt, and baking soda in a separate bowl.

Combine the dry ingredients with the wet mixture by stirring them in.

Fold in the chopped white chocolate, salted roasted pistachios, and dark chocolate.

Scoop the dough into a greased cupcake pan, filling each cup about three-quarters full.

Bake for about 14 minutes or until golden brown.

Cool the Pistachio Cookie Cups in the pan for a few minutes before transferring to a wire rack.