As with the original magic custard cake, the temperatures of the ingredients are important. If too hot it will cook the eggs, too cold it will harden the butter.
For folding in the whites, it is done with more of a gentle whisk/folding motion with the whisk since the batter is so runny.
YIELD: ONE 8″X8″ CAKETOTAL TIME: 1 HOUR 30 MINUTES
Preheat the oven to 325°F. Lightly butter or grease a 8″x8″ baking dish.
Melt the butter and set aside to slightly cool. Warm the milk to lukewarm and set aside.
In a separate bowl, whisk together the flour, pinch of salt and cocoa powder for 20 seconds. Set aside.
Whip the egg whites with vinegar to stiff peaks. Set aside.
Beat the egg yolks and sugar until light. Add vanilla extract, and mix
Add butter and mix about 2 minutes and or until evenly incorporated.
Mix in the flour/cocoa into the batter until evenly incorporated. (I’ve sifted to remove lumps.)
Gently whisk/beat in the milk until everything is well mixed.
Fold/gently-whip in the egg whites, 1/3 at a time. Repeat until all of the egg whites are folded in.
Pour the batter into the prepared pan and bake for 50-60 minutes.
Allow cake to completely cool before cutting and then dust with cocoa powder