Preheat your oven to 350°F (175°C). Grease and line an 8x8 inch baking pan with parchment paper, leaving some overhang on the sides for easy removal later.
In a medium saucepan, melt the butter over medium heat. Once melted, remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the melted butter and granulated sugar until well combined. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract until smooth.
Sift in the cocoa powder, all-purpose flour, salt, and baking powder into the wet ingredients. Gently fold the dry ingredients into the wet until just combined. Be careful not to overmix.
Gently fold the frozen raspberries into the brownie batter until evenly distributed. The raspberries will start to thaw as you mix, creating swirls of raspberry goodness throughout the brownies.
Pour the brownie batter into the prepared 8x8 inch baking pan and spread it out evenly with a spatula.
Place the pan in the preheated oven and bake for 25-30 minutes, or until the edges are set and a toothpick inserted into the center comes out with a few moist crumbs attached. Be careful not to overbake, as you want the brownies to be fudgy.
