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 well combined. Add eggs and vanilla extract, continuing to whisk until fully incorporated.
03 - Sift cocoa powder, all-purpose flour, salt, and baking powder into the wet mixture. Gently fold together using a spatula until just combined, being careful not to overmix.
04 - Blend cottage cheese in a food processor or with an immersion blender until completely smooth. Add egg yolk, sugar, and vanilla, processing until the mixture is creamy and uniform.
05 - Spread the brownie batter evenly into the prepared pan, smoothing the surface with a spatula. Spoon dollops of the cottage cheese mixture over the batter.
06 - Run a knife or skewer through the batters in a swirling motion, creating a marbled pattern. Be careful not to over-swirl to maintain distinct layers.
07 - Bake for 33 to 36 minutes until edges are set and a toothpick inserted in the center comes out with a few moist crumbs. The center should still be slightly fudgy.
08 - Allow brownies to cool completely in the pan before slicing. This ensures clean cuts and allows flavors to fully develop.