1-First, preheat your oven to 425°F (220°C) and line a baking tray with parchment paper. In a saucepan, heat 250 ml (1 cup) water and 90 g (6 tbsp) butter until it just boils, then remove from heat.

2-Next, sift 150 g (1 cup) plain flour with a pinch of salt and 2 tsp sugar in a bowl. Add the dry mix to the hot water and butter all at once, stirring over medium heat until the dough forms and pulls away from the pan sides. Let it cool for about 5 minutes, then beat in 3 to 4 large eggs one at a time until the dough is smooth and elastic.

3-Pipe the dough into 2.5-inch balls on the tray, spacing them 2 inches apart, and smooth the tips with a wet finger. Bake at 425°F (220°C) for 10 minutes, then reduce to 375°F (190°C) for another 10-15 minutes until golden and puffed.

4-While the pastry bakes, warm 250 ml (1 cup) milk, 175 ml (3/4 cup) heavy cream, and 2 tsp vanilla flavoring over medium heat without boiling. In another bowl, whisk 75 g (1/3 cup) caster sugar and 3 egg yolks until pale, then mix in 50 g (1/3 cup) flour. Gradually add this to the warm milk mixture, whisking constantly until it thickens.

5-Chill the custard to set it further. For the chocolate sauce, melt 113 g (3/4 cup) dark baking chocolate and 2 tbsp butter over low heat, then stir in 65 ml (1/4 cup) thickened cream and 2 tbsp sugar until smooth.

6-After baking, pierce a small hole in the base of each pastry to release steam and dry them briefly in the oven. Once cooled, fill each puff with 1-2 teaspoons of custard using a spoon or piping bag. Drizzle with chocolate sauce just before serving for the best results.