01 -
Heat the oven to 335°F (170°C). Take a 9-inch square pan and line it with parchment paper, ensuring all sides are covered.
02 -
Microwave butter in 30-second intervals until melted. In a big bowl, stir the melted butter with both sugars until combined well.
03 -
Add the eggs, yolk, and vanilla to the bowl, stirring slowly to avoid extra bubbles. Then add the cocoa powder and oil, mixing until the texture is smooth.
04 -
Scoop out a little mix and whisk in the food gel until it’s totally mixed in. Add this back to the main bowl, stirring gently until the color is even.
05 -
Using a spatula, fold in the flour, cornstarch, and salt until just combined, being careful not to leave dry streaks. Lastly, mix in the vinegar. If you like, toss in the white chocolate chips.
06 -
Spread the batter evenly into the lined pan. Bake for 20 to 25 minutes. When a skewer poked into the middle comes out with damp crumbs but not wet batter, it’s ready. Cool down completely before adding the top layer.
07 -
Beat the cream cheese and butter together until they look nice and smooth. Slowly add the powdered sugar, then whip at high speed till it’s fluffy. Finally, mix in the vanilla.
08 -
After the base has cooled down all the way, spread the frosting evenly over it. Cut into pieces and dig in.