01 -
Line a 9-inch square cake pan with parchment paper and preheat the oven to 180°C (350°F) or 160°C for fan-assisted ovens.
02 -
Melt the butter in the microwave in 30-second increments until completely melted.
03 -
Place the granulated sugar and light brown sugar in a large mixing bowl. Add the melted butter and whisk together until combined.
04 -
Add the eggs, egg yolk, and vanilla extract into the sugar mixture. Mix gently, avoiding overmixing to prevent incorporating air.
05 -
Whisk the vegetable oil and cocoa powder into the batter until completely combined. Be careful not to introduce air into the mixture.
06 -
Take a couple of tablespoons of the batter and mix with the red food coloring in a separate bowl. Incorporate this back into the main batter.
07 -
Using a rubber spatula or wooden spoon, fold in the flour, cornstarch, and salt until no dry flour remains.
08 -
Mix in the vinegar until fully combined.
09 -
If desired, fold in the white chocolate chips for added texture.
10 -
Pour the batter into the prepared cake pan and bake for 20-25 minutes, or until a skewer inserted into the center comes out with moist crumbs.
11 -
Allow the brownies to cool completely before frosting and slicing.
12 -
Beat the room-temperature butter and cream cheese together until smooth. Gradually add the powdered sugar and mix on high speed until light and fluffy. Add vanilla and beat briefly to combine.
13 -
Spread the cream cheese frosting evenly over the cooled brownies before slicing.