Preheat oven to 200ºC/400ºF/ Gas Mark 6. Grease a nine inch loaf tin and dust with flour. In a bowl whisk together cocoa and one cup boiling water until smooth. Cool to room temperature. In another bowl lightly combine the eggs, one fourth of the cocoa mixture and vanilla essence.
In another mixing bowl sift refined flour, baking powder, Sugar Free and salt and mix with electric beater at low speed for thirty seconds to blend. Or alternatively mix well using a wooden spoon. Add butter and remaining cocoa mixture.
Mix slowly until the dry ingredients are moistened. Continue to mix a little fast for one and half minutes. Scrape down the sides. Gradually add the egg mixture and beating well to incorporate all the ingredients well together.
Scrape down the sides. Transfer the batter into the prepared tin and smoothen the surface with a spatula. Bake in the preheated oven for forty minutes. Let the cake cool in the tin.
Loosen the sides with a small metal spatula and invert onto a greased wire rack and cool further before slicing and serving.