Place egg whites in a very clean bowl. The bowl should be super clean a pinch of grease may spoil your cake.
Place the bowl of egg whites over a double boiler and start whisking it till it is frothy.
Once frothy remove from double boiler and add half of the sugar and whisk till stiff peaks stage. Keep it aside.
In another vessel add in cream cheese, milk, sour cream, butter and just melt by placing it over the gas stove.
Add in the egg yolks one by one in the cream cheese mixture and mix properly with each addition.
Sieve in the flour and gently mix it till well combined. Strain the mixture for a smooth texture and add in the remaining sugar and again mix well.
Combine egg whites with the cream cheese mixture in 3 additions and add in vanilla extract
Pour this in a parchment paper lined tin and gently give it a tap to remove any air bubbles.
Bake this in a preheated oven at 160 degree in water bath for 45 minutes.
After 45 minutes let the cake cool in the oven itself and slowly unmold it.
Dust some cocoa powder over the cake and serve.
