Preheat the oven to 350℉ and prepare a baking sheet by greasing it with butter or lining it with parchment paper, tin foil or a silicone baking mat.
In a large bowl, add the butter and brown sugar. Using a hand mixer, mix on medium-high for 1-2 minutes or until incorporated and lightly fluffy. Add the white granulated sugar and mix again until incorporated.
Add the egg and vanilla extract and mix. Add the all purpose flour, salt and baking soda and mix for the last time (this can be done with a spatula instead of the hand mixer).
Using a wooden spoon or spatula, fold in the white chocolate chips and chopped pistachios until they are just incorporated.
Using a cookie scoop or spoon, distribute 1-2 tbsp of dough onto the prepared baking sheet, making sure they are evenly spread apart.
Bake the cookies for 10-12 minutes. The cookies will look slightly underbaked but remove them from the oven. Just make sure the bottom of the cookies are a light golden brown and then let them cool for at least 5-10 minutes. If you want, you can drizzle some melted white chocolate* on top for extra flavour. Enjoy!