For the choux pastry: preheat the oven to 210C/190C fan/gas 6.
In a heavy-based saucepan bring 300ml water and the butter to a boil. Once the butter has melted, take the pan off the heat, tip in the flour and beat with a wooden spoon. Return the pan to a medium heat and stir briskly until the dough is soft, shiny and comes cleanly from the sides of the pan.
Continue beating the dough with an electric hand whisk until it has cooled a little. Gradually beat in the eggs, a very small amount at a time, stopping when the pastry is sticky but not liquid.
Pipe balls of the choux pastry (about the size of a teaspoon) on a non-stick baking tray, about 4cm apart from each other.
Bake for 8 minutes and then reduce the oven to 180C/160C fan/gas 4 and bake for a further 10-15 minutes, or until golden brown and cooked through. Transfer to a cooling rack to cool.
For the pastry cream: put the milk, vanilla pod and seeds, cinnamon, cloves, bay leaf, star anise and nutmeg in a saucepan. Bring to a simmer then remove from the heat. Set aside to infuse for 20 minutes.
Whisk the sugar, egg yolks, flour and cornflour together in a bowl.
Pour the infused milk through a sieve into the yolk mixture, stirring all the time. Pour the mixture back into a clean pan and simmer over a medium heat for about 5 minutes, or until the taste of cornflour is removed. Pour into a clean bowl, cover and chill.
To assemble the dessert, put the cooled pastry cream in a piping bag. Using a small, sharp knife, mark each cooked choux bun with a cross. Push the nozzle of the piping bag into each cross and fill the buns with the pastry cream.
. Once all the buns are filled, grease a cone-shaped mould with butter or line it with acetate or baking parchment. Melt a little dark chocolate (for sticking) in a bowl in the microwave, mixing it with a rubber spatula every 5-10 seconds until smooth.
. Dip the tips of the buns in the melted chocolate and place them tip side-down in the cone, ensuring each layer is level. Continue until the desired height is reached. Chill for at least 3 hours to ensure the chocolate has set.
. For the chocolate sauce: break both types of chocolate into pieces and place in a heatproof bowl with the butter. Melt in the microwave on a medium setting, checking every 5 seconds to ensure you don’t overcook the chocolate.
. Warm the milk in a small saucepan and gradually stir it into the melted chocolate mixture.
. Turn out the chocolate pyramid onto a cake stand, pour over the chocolate sauce and serve.