Preheat the oven to 165ºC.
In a small bowl, beat your egg until combined then pour ½ into a larger mixing bowl (you only need ½ for this recipe so save the other ½ for something else).
Add the sugar then use an electric whisk to whisk until the eggs are very pale and fluffy.
Add the vanilla and whisk again for a couple of seconds.
Sift in the cocoa powder, plain flour and salt and whisk very briefly until just combined.
Add the melted butter and whisk for a final time, again until just combined.
Pour into an individual ramekin then place the ramekin in a larger baking dish.
Fill the baking dish with hot water until the water reaches halfway up the ramekin.
Bake for 25-35 minutes until the top is firm and set but the pudding still gives when gently pressed.
Dust with icing sugar before serving.
