The night before: prepare the choux buns the chocolate mousse and the coffee syrup.
Pre-heat the oven to 180 °C (Gas 6). Bring the water to boil with the salt, butter and sugar. Remove from the heat, pour all the flour in at once and beat to form a ball that should leave the sides of the pan. Add the eggs whole, one by one, stirring after each egg. Fill a piping bag and pipe plum-sized blobs onto a baking tray. Place in the oven and bake for about 20 minutes, then place on a wire rack to cool.
Break the chocolate into pieces and melt on low heat. Mix the egg yolks, sugar, melted chocolate and cream. Beat the egg whites until firm. Fold gently into the chocolate and leave in the fridge.
Bring the coffee and the sugar to boil on low heat. Add the coffee extract and the walnut halves.
The next day: garnish and ice the choux buns
Make a hole in the bottom of each choux bun. Using a piping bag, pipe chocolate mousse in to each bun until half full. Slip a walnut half and a little coffee syrup into each choux bun and top up the filling with chocolate mousse. Keep the rest of the coffee syrup in the fridge.
Mix the egg white, icing sugar and coffee extract together. Ice the choux buns and scatter crushed walnut over the top. Keep in a cool place until serving time.
Enjoy the choux buns accompanied by the coffee syrup served very cold and in small liqueur glasses.
Author and photograph: Philippe Barret