Transfer the paste to a large piping bag fitted with a 1.5cm/½in fluted nozzle and let the mixture to cool for about five minutes in the bag to stiffen slightly before you begin the piping.

Put the choux on wire racks to cool completely. For the pistachio crème pâtissière, pour the milk into a pan, add the pistachio paste and bring to the boil, then remove from the heat.

Bring to the boil, tip in the flour, then remove from the heat. Stir vigorously. When a smooth paste develops, return the pan to the heat, stirring. The mixture will dry out a little and form a ...