Put the water and butter in a saucepan and set to simmer till butter melts.  Remove from heat, add in the flour and baking powder, return to the heat and cook with a spoon until the mixture binds and leaves the pan clean. Remove from heat and allow cooling before adding in the eggs. Beat in the eggs gradually until a thick smooth consistency is obtained. 

Pipe the choux paste into desired size, sift some icing sugar on top and bake at 175°C until pastries are puffed, browned and dry.

For the Chocolate crème patisserie:

Whisk the milk and vanilla essence in a sauce pan and bring gently to the boil. In a separate recipient, whisk together the yolks and egg, cocoa powder, Caster sugar and corn flour. Pour over halve of the boiling milk whisking continuously.

Return the milk-egg mixture to the pan and cook till custard starts boiling and thickens. Remove from heat, whisk in the dark chocolate and mix till it melts, stir in the butter. 

Transfer into a bowl, cover with cling film to avoid a skin from forming and allow cooling completely. 

For the Chocolate glaze:

Place all ingredients in a bain-marie until all ingredients are well blended.