Preheat oven to 350°F and line a 13×9-inch baking pan with parchment paper, letting it hang over two sides; grease with cooking spray.
In a stand mixer bowl with paddle, cream together butter, brown sugar, and white sugar until light and fluffy, about 2 minutes.
Add vanilla extract and salt; beat to combine.
Add eggs one at a time, beating well after each addition.
Beat in flour and baking powder just until combined, then fold in chocolate chips. Set cookie batter aside.
Whisk melted butter, sugar, cocoa powder, vanilla extract, red food coloring, white vinegar, eggs, and salt in a large bowl.
Fold flour into the red velvet mixture just until combined.
Alternately spoon scoops of cookie batter and red velvet brownie batter into the prepared pan.
Bake 30-40 minutes until cookie dough is golden and brookies are fully set.
Remove from oven immediately, sprinkle with large-flake sea salt, and let cool completely in pan before slicing.