Preheat your oven to 350°F (180°C) and prepare a 9-inch square cake pan with parchment paper.
Melt the unsalted butter in a microwave-safe bowl until fully melted, then let it cool slightly.
Combine the melted butter with granulated sugar and light brown sugar, whisking until smooth.
Incorporate the large eggs, egg yolk, and vanilla extract into the sugar-butter mixture.
Add vegetable oil and cocoa powder, mixing until well combined and glossy.
Mix red food coloring with a couple of tablespoons of the brownie batter, then blend it back into the main batter.
Fold in dry ingredients: all-purpose flour, cornstarch, and salt until no lumps remain.
Pour in the vinegar and mix well to combine.
Fold in white chocolate chips if using.
Transfer the batter into the prepared pan and bake for 20-25 minutes.
Cool the brownies completely in the pan for about 30 minutes.
Prepare the cream cheese frosting by beating cream cheese and unsalted butter until smooth.
Gradually add powdered sugar, mixing on low speed before increasing to high until light and fluffy.
Add vanilla extract to the frosting and beat briefly.
Spread the cream cheese frosting generously over the cooled brownies and if desired, sprinkle red brownie crumbs on top.
