01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, ensuring it covers the bottom and sides for easy removal.
02 - In a large bowl, whisk melted butter and granulated sugar until smooth and fully incorporated. Add eggs and vanilla extract, whisking until the mixture is well combined and slightly thickened.
03 - Sift cocoa powder, all-purpose flour, salt, and baking powder into the wet mixture. Fold gently with a spatula until just combined, being careful not to overmix as this can toughen the brownies.
04 - In a separate bowl, blend cottage cheese until completely smooth using a food processor or immersion blender. Add egg yolk, sugar, and vanilla extract; continue blending until the mixture is creamy and uniform in texture.
05 - Pour the brownie batter into the prepared baking pan, using a spatula to spread it evenly and create a smooth surface.
06 - Spoon dollops of the cottage cheese mixture over the brownie batter in an even pattern. Draw a knife or skewer through both batters in a gentle figure-eight or circular motion to create a marbled effect without over-blending.
07 - Bake for 33-36 minutes, checking for doneness by inserting a toothpick into the center. The edges should be set and the toothpick should emerge with a few moist crumbs—avoid overbaking for fudgy texture.
08 - Allow the brownies to cool completely in the pan before slicing. This ensures clean edges and allows the flavors to fully develop. For easiest cutting, refrigerate for 30 minutes before serving.