Line a 9-inch square cake pan with parchment paper and preheat the oven to 350°F / 180°C (160°C fan assisted).

Melt butter in the microwave in 30-second increments until completely melted.

Put the white sugar and light brown sugar in a large mixing bowl, then add the melted butter and whisk together until combined.

Add the eggs, egg yolk and vanilla and mix together. Be careful not to overmix - we are not trying to add air into the mixture as that will make the brownies cakey.

Add the vegetable oil and the cocoa powder to the brownie batter and whisk together gently until completely combined - again we are not trying to incorporate air.

Take a couple of tablespoons of the batter and put them into a small bowl, add your red gel food coloring to this bowl and mix it in until the gel is all incorporated and there are no lumps. Add this mixture into the main bowl of batter and mix until combined.

Switch from a whisk to a rubber spatula or wooden spoon and fold in the dry ingredients including flour, cornstarch and salt.

When there are no more lumps of flour, add the vinegar and mix in well.

Optional: If you like, you can add some white chocolate chips at this stage. I decided I liked the brownies better without.

Pour the brownie batter into the prepared cake pan and bake for 20 - 25 minutes or until a skewer comes out with just moist crumbs on it.

Remove from the oven and let cool completely before attempting to frost and slice.

Beat the room temperature butter and cream cheese together until smooth and combined.

Add the powdered sugar and mix in slowly, once the dust cloud settles, turn your mixer onto high speed and beat for a few minutes until light and fluffy.

Add the vanilla and beat in for another few seconds.

Spread over the red velvet brownies before slicing.