Preheat the oven to 350°F. Line an 8×8-inch baking pan with parchment paper, leaving a little overhang on two sides.
Melt 1/2 cup butter in a microwave-safe bowl in short bursts or in a small saucepan over low heat. Let it cool for 2 to 3 minutes so it is warm, not hot.
Whisk the melted butter and sugar in a large mixing bowl for about 1 minute until glossy and smooth.
Add the eggs one at a time, whisking for 20 seconds after each addition. Stir in the vanilla extract until the mixture looks smooth and slightly thick.
Add cocoa powder, flour, salt, and baking powder directly to the bowl. Fold gently with a spatula until no dry streaks remain.
Stir in 1/2 cup chocolate chips or chunks.
Spread the batter evenly in the prepared baking pan.
Bake for 28 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Let the brownies cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
Dust with powdered sugar, if desired, then cut into 16 squares and serve.