Preheat to 220 °C (200 °C fan/Gas 7) and line a baking sheet with nonstick paper.

In a small saucepan over high heat, bring the butter and water to a rolling boil. Remove from heat, add all the flour at once, and beat quickly with a wooden spoon until it forms a smooth, thick dough.

Let the dough cool for 1 minute, then beat in the beaten eggs a little at a time, mixing well after each addition until the dough is thick, glossy, and holds its shape.

Spoon or pipe 12 mounds of dough (about a tablespoon each) onto the prepared sheet, spacing them well apart. Brush the tops with the extra beaten egg. Bake for 10 minutes at 220 °C, then lower the oven to 190 °C (170 °C fan/Gas 5) and bake another 20 minutes.

Turn off the oven and split each bun in half. Place them cut‑side up on the tray and return to the cooling oven for 15–20 minutes to dry out completely.

Meanwhile, warm the cream in a small pan until it just starts to steam. Remove from heat, stir in the chocolate pieces until smooth, and let it sit at room temperature to thicken slightly.

Once the shells are crisp, dip each top half into the chocolate sauce. Set them on a wire rack to let the chocolate set.

Pour the remaining 200 ml cream into a bowl and whisk until it holds soft peaks.

Spoon or pipe a generous dollop of whipped cream into each bottom half, then sandwich with a chocolate‑dipped top. Serve right away and watch them disappear!