Begin by preheating your oven to 350°F (175°C). Prepare a 9x13 inch baking pan by greasing it with a thin layer of butter and lining it with parchment paper, allowing excess paper to hang over the edges.
In a medium saucepan, melt the unsalted butter over low heat until fully liquid. Once melted, remove the saucepan from heat and carefully stir in both the granulated sugar and packed brown sugar. Mix until the sugars are completely incorporated and create a smooth mixture.
Allow the butter-sugar mixture to cool slightly to prevent cooking the eggs. Then, whisk in the eggs, adding them one at a time and ensuring each egg is fully blended into the batter before introducing the next. Finally, mix in the pure vanilla extract for added flavor.
In a separate mixing bowl, sift together the unsweetened cocoa powder, all-purpose flour, baking powder, and salt.
Gradually fold the dry ingredients into the wet mixture, stirring delicately until just combined. Be cautious not to overmix.
Carefully incorporate the semi-sweet chocolate chunks and dark chocolate chips into the batter.
Pour the luscious brownie batter into the prepared baking pan, using a spatula to spread it into an even layer.
Place the pan in the preheated oven and bake for 25-30 minutes. The brownies are done when a toothpick inserted into the center comes out with a few moist crumbs.
After baking, remove the brownies from the oven and let them cool in the pan for about 10 minutes. Using the overhanging parchment paper, carefully lift the brownies out of the pan and transfer them to a wire rack to cool completely.
Once fully cooled, cut the brownies into squares. Serve and enjoy!
Notes
Enjoy these brownies warm, or at room temperature. For a luxurious treat, top them with a scoop of vanilla ice cream or sprinkle with flaky sea salt for a delicious contrast.