In a large bowl, cream the softened butter with the brown sugar and granulated sugar until light and fully combined.
Add the eggs one at a time, mixing just until incorporated after each addition.
Stir in the vanilla extract until the mixture looks smooth.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt until evenly combined.
Gradually add the dry ingredients to the wet ingredients, mixing on low speed and stopping as soon as no flour streaks remain.
Fold in the chocolate chips or chunks by hand until evenly distributed.
Cover the dough and refrigerate for at least one hour.
Preheat the oven to 350°F and line baking sheets with parchment paper.
Scoop the dough into two-tablespoon portions and gently roll into balls without compressing.
Place the dough balls about three inches apart on the prepared baking sheets.
Bake one tray at a time for 10 to 12 minutes, rotating the pan halfway through baking.
Remove the cookies when the edges are set and the centers still appear slightly soft.
Let the cookies rest on the baking sheet for five minutes before transferring to a wire rack to cool completely.