01 -
Preheat the oven to 350°F (160°C fan). Line a 9-inch square pan with parchment paper.
02 -
Melt the butter fully in the microwave in short 30-second bursts. Stir it together with both types of sugar in a large bowl until smooth.
03 -
Carefully stir in eggs, the spare yolk, and the vanilla. Don’t overmix, or the brownies might lose their fudgy texture. Blend in the oil and cocoa powder until just mixed.
04 -
In a small bowl, combine a couple of tablespoons of the batter with the red food dye. Once mixed, return it to the main mixture and fully stir in.
05 -
Carefully stir in the flour, cornstarch, and salt using a spatula or wooden spoon. Add vinegar to the mix and stir gently. Toss in the chocolate chips if you’re using them.
06 -
Pour the batter into your lined pan. Bake for 20–25 minutes, checking with a skewer that should come out with just a little moisture. Let it cool completely before topping.
07 -
Beat the butter and cream cheese together until smooth and creamy. Add the icing sugar slowly and beat until fluffy. Finally, mix in the vanilla.
08 -
Spread the frosting on the completely cooled brownies. Slice them into squares and enjoy!