Chocolate Guinness Magic Cake

Preheat the oven to 325u0b0F. Grease an 8 x 8 baking tray and set aside.
Melt the butter and let cool slightly. Set aside.
Combine the milk and the beer in a saucepan until lukewarm.
Mix the flour and 1/2 cup cocoa together in a bowl and set aside. Using a stand mixer, whip the egg whites and the vinegar until you reach stiff peaks. Set aside.
In a large bowl, beat the egg yolks with the confectioners sugar until it turns smooth and light in color, about 5 minutes. It'll be really stiff at first but will loosen up as you continue to whisk. Add the melted butter and whisk gently until combined. Add the flour mixture and mix until smooth.
Gently pour in the milk/beer mixture and whisk until smooth. Add the egg whites a little at a time, whisking gently. This is where things look a little funky but as long as you break down the large lumps of egg white, then it'll be fine.
Pour the mixture into the prepared baking tray until about 1/2 inch from the top. Place it on a larger baking tray and put it in the oven. Bake for about 50 minutes and the middle is wobbly but firm looking.
The cake will be much easier to cut and serve when left to cool. I cooled mine for 24 hours, which was really hard (I sooo wanted to taste it). You could cut into it after an hour or two in the fridge. Dust with cocoa powder and serve with whipped cream or on its own.
Recipe adapted from White On Rice Couple.