"Inspired (and cribbed) largely from Brooke's Best Bombshell Brownies and Eggless Peanut Butter Cookies, both recipes found here on Allrecipes, I concocted this amazing treat. They turned out so fantastic, I thought they deserved their own recipe."
Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13-inch baking dish.
Combine 2 1/2 cups white sugar, 1 cup melted butter, and vanilla extract in a large bowl. Beat in eggs one at a time with an electric mixer, mixing well after each addition until thoroughly blended.
Sift 1 1/2 cups flour, cocoa powder, and salt together in a bowl. Stir flour mixture gradually into butter mixture until blended. Spread batter evenly into the prepared baking dish.
Bake in the preheated oven until an inserted toothpick comes out clean, 35 to 40 minutes.
Combine milk and vinegar in a large bowl and let stand for 5 minutes until milk sours. Add 1/2 cup butter, peanut butter, 1/2 cup white sugar, and brown sugar; stir until mixture is smooth and fully combined.
Sift 1 1/4 cups flour, baking soda, baking powder, and salt together in a small bowl. Mix into peanut butter mixture until well blended.
Spread peanut butter mixture over warm brownies. Drizzle melted chocolate chips on top. Refrigerate for 1 to 2 hours before cutting into squares.