01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, ensuring excess paper hangs over edges for easy removal.
02 - In a large bowl, whisk melted butter and granulated sugar until completely smooth. Add eggs and vanilla extract, whisking thoroughly until fully incorporated.
03 - Sift cocoa powder, flour, salt, and baking powder into the wet mixture. Fold gently with a spatula until just combined; avoid overmixing to prevent dense texture.
04 - Blend cottage cheese in a food processor or with an immersion blender until completely smooth. Add egg yolk, sugar, and vanilla; process until silky and uniform.
05 - Spread brownie batter evenly into the prepared pan, using an offset spatula to create a smooth surface.
06 - Drop spoonfuls of cottage cheese mixture over the brownie batter. Draw a knife or skewer through both mixtures in a figure-eight motion to create a marbled pattern.
07 - Bake for 33-36 minutes until edges are firm and slightly pulled away from pan sides. A toothpick inserted in center should emerge with a few moist crumbs, not wet batter.
08 - Allow brownies to cool completely in the pan before slicing. This ensures clean cuts and allows flavors to fully develop.