Preheat the oven to 350°F and slightly grease a 9 x 6" ceramic bakeware.
Using an electric mixer, beat the egg whites until soft peaks are formed.
Gradually incorporate the sugar until firm peaks are formed. By the end, you should be able to slowly turn the bowl upside down without the eggs to fall.
Reduce the speed of the mixer and incorporate the egg yolks, the cocoa powder and a pinch of salt.
Using a spatula, gently fold in the flour. Try not to overmix.
Slowly transfer the batter in a slightly greased pan and bake for 30 minutes or until a toothpick comes out clean.
In the meanwhile, combine all the ingredients for the sauce in a small saucepan.
Bring to boil and simmer for a few minutes until the sauce thickens up and becomes syrupy, stirring constantly to avoid lumps. Remove from the heat and let it cool down on the counter. Mix again before pouring.
When ready, remove the cake from the oven and let it cool down for 5-10 minutes before pouring the sauce over it.