Melt the cooking chocolate with the butter in a bain-marie. Beat the eggs with the sugar using a mixer until they become fluffy. Remove melted chocolate and butter from the bain-marie and blend in with the eggs and sugar stirring softly with a spoon. Gradually add the flour. Butter and sprinkle sugar in a baking tin, 10x27 cm and pour in the brownies mixture; bake in a pre-heated oven at 180ο C for 20 minutes. The cake should be moist. Leave to cool slightly and remove from the tin. Cut in squares.
 
If we want the centre of the cake to be soft, each time we serve, we can reheat it in the oven for a few minutes.