Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on two sides to form a sling. Lightly grease the parchment and sides of the pan with cooking spray or butter.

In a large mixing bowl, whisk together the melted, slightly cooled butter, granulated sugar, and light brown sugar until glossy, thick, and well combined.

Add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract and distilled white vinegar until fully incorporated.

Sprinkle in the cocoa powder, baking powder, and fine sea salt. Whisk until no dry cocoa streaks remain; the mixture will be somewhat thick.

Add the red gel food coloring and whisk until the color is uniform. Start with 1 tablespoon and add more as needed for a bright red shade, keeping in mind the color will dull slightly as it bakes.

Using a rubber spatula, gently fold in the all-purpose flour just until combined; do not overmix. Fold in the white chocolate chips, if using. Pour about 3/4 of the batter into the prepared pan and spread into an even layer. Set the remaining batter aside for swirling.

In a medium bowl, beat the softened cream cheese with a hand mixer until smooth and creamy. Add the 1/4 cup granulated sugar, egg yolk, and 1/2 teaspoon vanilla extract. Beat until the mixture is silky and mostly lump-free.

Spoon the cream cheese mixture over the brownie batter in the pan in large dollops across the surface. Spoon the reserved red velvet brownie batter between and on top of the cream cheese dollops. Use a butter knife or thin spatula to gently drag through the batter in long S-shapes in both directions, creating a swirl. Do not over-swirl; you want distinct ribbons of red and white.

Place the pan on the center oven rack and bake for 28–35 minutes. Start checking around 27 minutes. The brownies are done when the edges are set, the top looks slightly shiny, and a toothpick inserted about 2 inches from the edge comes out with a few moist crumbs but no wet batter. The center may look slightly soft; it will firm up as it cools.

Let the pan cool completely on a wire rack, about 1 1/2 hours. Once fully cool, use the parchment sling to lift the brownies out of the pan and transfer to a cutting board. Slice into 16 larger bars or up to 24 smaller squares, wiping the knife clean between cuts for the neatest edges.