Preheat oven to 350 deg. Grease a 9 inch. cake tin, lightly dust with flour.
Break chocolate into small pieces and melt it with the water in a double boiler
Separate egg whites and yolks. With an electric mixer whisk the eggs whites until forming stiff peaks, add half of the sugar while mixing.
In a separate bowl whisk the egg yolks with the remaining sugar for one minute using the mixer.
Add gradually the vegetable oil, one spoon at a time and mix well.
Add melted chocolate and mix well. Transfer to the bowl containing the whisked egg whites.
Sift in the flour and baking powder, add vanilla extract
Fold everything together using a spoon or a rubber spatula.
Transfer to cake tin and bake at 350 degrees until a wooden pick inserted in center comes out clean, approximately 45 to 60 minutes
Leave the cake to cool in the tin, it could be refrigerate for one hour before slicing.
When completely cold, remove the top of the cake, slice through the middle to make two layers. Break chocolate in small pieces and melt with butter using the double boiler like before . Let mixture cool before using it. Use half of the melted chocolate for filling and half for frosting. Place the cake in the refrigerator to harden the icing.