01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl. Set aside.
03 - Beat softened butter, granulated sugar, and brown sugar in a large bowl until light and fluffy, about 2-3 minutes.
04 - Beat in eggs one at a time, then add vanilla extract.
05 - Gradually mix dry ingredients into wet ingredients until just combined.
06 - Fold in chocolate chips, dark chocolate chunks, and walnuts if using.
07 - Scoop heaping tablespoons of dough onto prepared baking sheets, spacing about 2 inches apart.
08 - Bake for 10-12 minutes until set at edges but still soft in center.
09 - Let cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.