Preheat oven to 180°C.
Grease an ovenproof baking dish.
Sift flour and cocoa into a large bowl and add the sugar.
Whisk butter, milk, egg and vanilla essence together and slowly add to the flour mixture, until well mixed and smooth.
Pour into the baking dish and smooth down with the back of a spoon.
Sift cocoa powder over pudding and scatter the brown sugar over the top.
Pour boiling water over the back of a large metal spoon over the entire pudd ing covering the cocoa and sugar.
Bake for 35 - 40 minutes or until sponge is cooked.