Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
In a large bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy.
Beat in eggs, one at a time, followed by vanilla extract.
In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt. Gradually mix dry ingredients into wet ingredients until just combined.
Fold in chocolate chips (and optional nuts).
Scoop dough onto prepared baking sheets, spacing about 2 inches apart.
Bake for 10–12 minutes, until edges are set but centers remain soft.