Cake: Preheat the oven to 200 degrees C. Grease and line with baking paper two 20cm round sandwich tins.
Put the self raising flour, sugar, cocoa, baking powder and salt in a bowl then mix well.
Pour over vegetable oil, vanilla and vinegar and then the water. Beat thoroughly with a whisk. Pour the mixture into the two prepared round sandwich tins.
Bake for about 25 minutes in the preheated oven or until firm and springy to the touch and a skewer comes out clean when inserted into the middle. Leave to cool in the tin for 5 minutes then turn out on to a cooling rack, remove the baking paper then leave to cool completely while you make the icing.
Fudge Icing: Put all the icing ingredients in a saucepan and slowly bring them to the boil over a low heat, stirring constantly. Boil for one minute then remove from heat.
Leave the icing to cool. Beat the icing occasionally while it cools, so that lumpy crystals don't form. You can add vanilla extract at this point if you like.
To Assemble: Once the icing has cooled, spread 1/3 of the mixture over the first layer of the cake. Place the other layer on top and cover with the remaining icing. Use a spatula or palette knife to spread it round the sides.
This can very easily be made gluten free by using gluten free flour and baking powder. You may need to increase the amount of water you add, as gluten free flour can be more absorbent.