Line a 9x13 inch pan with parchment paper and preheat oven to 350F.
Melt butter in microwave and let cool slightly.
Whisk both sugars with melted butter until combined.
Add eggs, egg yolk, and vanilla, mixing gently without overbeating.
Whisk in vegetable oil and cocoa powder until combined.
Mix red gel food coloring into 2 tablespoons of batter, then stir back into main bowl until color is even.
Switch to rubber spatula and fold in flour, cornstarch, and salt until no lumps remain.
Fold in vinegar until well mixed.
Pour batter into prepared pan and bake 20-25 minutes until skewer comes out with moist crumbs.
Cool completely at room temperature, about 2 hours.
Beat cream cheese and butter together until smooth.
Add powdered sugar and beat on high speed for 3-4 minutes until light and fluffy.
Beat in vanilla until incorporated.
Spread frosting evenly over cooled brownies.
Cut into squares with a sharp knife, wiping blade between cuts.