Put the milk and water, butter and salt into a pan.
Heat gently until the butter has melted then bring to the boil.
Remove from the heat, add the flour and stir until smooth.
Cook for 1 minute, stirring.
Cool the mixture slightly, then gradually beat in the eggs.
Beat until the mixture leaves the sides of the pan.
Put the paste into a large piping bag fitted with a 1/2 inch plain pipe.
Dampen some baking trays.
Pipe 9 balls of 1 1/2 inch diameter and 9 balls of 1/2 inch diameter.
Bake at 400°F, Gas Mark 6 for 25-30 minutes until crisp and golden.
Make a slit in each bun so the steam can escape.
Cool on a wire rack.
Whisk the egg yolks with the sugar for the pastry cream until pale.
Blend in the flour and a little of the milk.
Boil the rest of the milk then pour on to the egg mixture, stirring well.
Return to the pan and cook for 2-3 minutes, stirring.
Cool slightly.
Whisk the egg whites until stiff then fold into the pastry cream with the vanilla essence.
When cold, use to fill the choux buns.
Melt the chocolate with the butter for the glace icing in a bowl placed over a pan of hot water.
When melted, stir in the icing (confectioners') sugar.
Add just enough water to make a thick glace icing.
Use to coat the top of the large buns.
Place a small bun on top of each and coat with icing.
Leave to set.
Beat together all the ingredients for the butter icing.
Leave in a cold place until stiff enough to pipe.
Using a small rose pipe and a forcing bag, pipe rosettes of chocolate butter-cream round the bases of each small bun to give a wreath effect.