Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
In a microwave-safe bowl, melt the butter until smooth. Let it cool slightly.
In a large bowl, whisk together the melted butter and granulated sugar until fully combined. Add in the eggs, one at a time, whisking well after each addition. Stir in the vanilla extract.
In a separate bowl, sift together the cocoa powder, flour, baking powder, and salt.
Gradually add the dry ingredients into the wet mixture, folding gently with a spatula until just combined. Be careful not to overmix; you want the batter to be thick and fudgy.
Fold in the chocolate chips or chunks evenly throughout the dough.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheets, spacing them about 2 inches apart. Bake for 9-11 minutes, or until the edges look set but the centers still appear soft.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.