Method

1. Preheat the oven to 220C/425F/Gas 7.

2. Grease a ramekin with butter and lightly dust with cocoa powder.

3. Whisk the egg whites until stiff peaks form when the whisk is removed, then gently fold in the custard.

4. Run your fingernail or the end of a teaspoon around the inside edge of the ramekin to loosen the soufflé from the side. Place onto a baking sheet and transfer to the oven to bake for 8-10 minutes, until risen and golden-brown.

5. To serve, transfer the soufflé onto a plate and dust with icing sugar.