01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, ensuring paper overhangs edges for easy removal.
02 - Whisk melted butter and granulated sugar in a large bowl until smooth. Add eggs and vanilla extract, whisking until thoroughly combined.
03 - Sift cocoa powder, flour, salt, and baking powder into the butter mixture. Fold gently until just incorporated, being careful not to overmix.
04 - Blend cottage cheese until completely smooth using a food processor or immersion blender. Add egg yolk, sugar, and vanilla extract, blending until uniform.
05 - Spread brownie batter evenly in the prepared pan. Drop cottage cheese mixture in dollops over the surface, then use a knife to create a marbled pattern by swirling gently.
06 - Bake for 33 to 36 minutes until edges are set and a toothpick inserted in the center emerges with moist crumbs. Avoid overbaking for fudgy texture.
07 - Allow brownies to cool completely in the pan before slicing. This ensures clean cuts and optimal texture development.