1. In a saucepan over medium heat, bring water, butter, and salt to a gentle boil. Remove from heat and stir in flour all at once. Return to heat and stir until a dough ball forms. Cool 5–10 minutes.

2. Beat in eggs one at a time until dough is glossy. Pipe or spoon onto a parchment-lined tray.

3. Bake at 200°C (390°F) for 20–25 minutes. Do not open oven during baking. Pierce bottoms to release steam and let cool.

4. Heat milk until steaming. In a bowl, whisk egg yolks, sugar, and cornflour. Slowly temper in the hot milk. Return to pan and cook until thickened.

5. Stir in butter, vanilla, and pistachio paste. Cool completely. Fold in whipped cream to make crème diplomate.

6. Pipe the pistachio crème into cooled choux buns using a small round piping tip.

7. Heat cream to a simmer and pour over chopped chocolate. Let sit, then stir until smooth to make ganache.

8. Dip bun tops in ganache. Garnish with crushed pistachios.

9. Chill buns for 30 minutes before serving.