Preheat the oven to 180°C (fan-forced). Prepare 4 small coffee cups by greasing with softened butter using kitchen paper, making sure the whole surface is covered. Add 1 tablespoon of cocoa powder into the cup then tip out any excess cocoa powder and place the cups on a tray ready for the oven.

In a mixer, whisk the egg whites until soft peaks begin to form. Gradually add caster sugar until stiff, then gently fold in the chocolate custard. Spoon the mixture into each cup.

Flatten the mixture by sliding the back of a knife across the rim of the cup. Using the tip of your thumb, swipe around the cup rim to make a slightly release the body of the souffle from the cup.

Bake for 8 to 10 minutes and dust with icing sugar to serve.