01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper.
02 - Whisk melted butter and sugar in a large bowl until smooth. Add eggs and vanilla, mixing until fully incorporated.
03 - Sift flour, cocoa powder, and salt into the wet mixture. Fold gently until just combined. Stir in chocolate chips.
04 - Blend cottage cheese until completely smooth. Whisk in egg yolk, sugar, flour, and vanilla until fully incorporated.
05 - Spread brownie batter evenly in the prepared pan. Dollop cottage cheese mixture on top in spoonfuls. Use a knife to gently swirl for a marbled effect.
06 - Bake for 32-36 minutes until a toothpick inserted in the center comes out with moist crumbs.
07 - Allow brownies to cool completely in the pan before slicing into squares.