Preheat your oven to 350°F (175°C). Grease an 8x8-inch baking pan or line it with parchment paper for easy removal.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until well combined.
In a large bowl, mix the melted butter and sugar until smooth. Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.
Gently fold in the blueberries, ensuring they are evenly distributed throughout the batter.
Pour the batter into the prepared baking pan and spread it evenly.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.