Steps
1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. In a mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
3. Add the vanilla extract and egg yolk, mixing until well combined.
4. In another bowl, whisk together the flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms.
5. Fold in the chopped pistachios and chocolate chips if using.
6. Scoop tablespoon-sized portions of the dough onto the prepared baking sheet, spacing them about 2 inches apart.
7. Bake for 10-12 minutes or until the edges are set and the centers are slightly soft.
8. Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.