Preheat the oven to 350℉ and prepare a baking sheet by greasing it or lining it with tin foil or a silicone baking mat.
In a large bowl, blend the pistachio butter and egg together using a whisk or hand mixer. Add in the vanilla extract and dry ingredients and mix again until combined.
Depending on the consistency of the pistachio butter, you may need to add 1-2 tbsp of water to make the dough moist and sticky. Fold in the white chocolate chips.
Using a cookie scoop or spoon, scoop 1-2 tbsp of batter onto the baking sheet. Repeat this, making sure the cookies are evenly spaced. Using a wet fork or spoon, gently press on the cookies until they are about 1 inch thick. Sprinkle chopped pistachios on top (optional).
Bake for 12-15 minutes or until the bottoms of the cookies are golden brown.
Allow the cookies to cool for 5-10 minutes before removing from the baking sheet. Enjoy!