Whisk together the cocoa powder, flour, baking soda and pinch of salt, and then stir into the pan; when mixed (this will be a very dry mixture, and not wholly blended at this stage), remove from the heat.
07In a bowl or jug, whisk the eggs with the vanilla extract and then mix into the brownie mixture in the pan.08Stir in the chopped chocolate and quickly pour and scrape into a foil-lined baking tin or disposable foil pan, spreading the mixture with a spatula, and cook in the preheated oven for about 20 to 25 minutes. It will look set, dark and dry on top, but when you feel the surface, you will sense it is still wibbly underneath and a cake tester will come out gungy. This is desirable.09Transfer the pan to a rack to cool a little before cutting into 16 pieces and dusting with confectioners' sugar. I love these gorgeously warm. But then again, I love them cold, too. Actually, when cold they are properly speaking more brownie-like: gooily tender within and moreishly chewy on top.10Make Ahead Note: The brownies can be made up to 3 days ahead and stored in airtight container. Will keep for total of 5 days.11Freeze Note: The brownies can be frozen for up to 3 months in airtight container, layered with baking parchment. Thaw overnight in cool place.