Preheat your oven to 350°F and line a 9x13-inch baking pan with parchment paper.
In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined.
Add eggs one at a time, mixing gently after each addition, then stir in vanilla extract.
In a separate bowl, whisk the flour, cocoa powder, baking powder, and salt so everything is evenly distributed.
Gradually add the dry ingredients to the wet ingredients, stirring just until no streaks of flour remain.
Fold in the chocolate chunks gently to avoid overmixing the batter.
Pour the batter into your prepared pan and smooth the top.
Bake for 30-35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.