For reliable results, work at a steady pace so your whipped egg whites and cream do not get too warm!

Separate eggs and yolks while eggs are cold. Place whites in a large bowl and yolks in a small bowl. Leave whites while you prepare other ingredients. (Note 4)

Whisk yolks until uniform.

Melt chocolate and butter - Place chocolate in a microwave-proof bowl with the butter. Melt in the microwave in 20 second bursts, stirring in between, until smooth. (Stir in optional flavourings at this point, but read Note 6 first). Set aside to cool slightly while you proceed with other steps - we want it at room temperature but still pourable.

Whip cream - Beat cream until stiff peaks form, being careful not to over-whip (see video).

Whip whites - Clean the whisks. Add sugar into the egg whites bowl. Beat until firm peaks form. GOAL - flopping "elf hat"! (see video and Note 5 for what this means).

Yolks and cream - Fold egg yolks into cream using a rubber spatula - 8 folds max. Some streaks is fine.

Check chocolate temperature - The chocolate should be cooled to room temperature but still runny (minimum 35°C / 95°F; ideal 40°C / 104°F). If too cool or thick, microwave in burst of 5 seconds at a time until runny.

Chocolate into cream - Pour chocolate into cream yolk mixture. Fold through - 8 folds max. Some streaks here are ok.

Fold in egg whites - Add 1/4 of beaten egg whites into chocolate mixture. Fold through until incorporated - "smear" the spatular across surface to blend white lumps in - aim for 10 folds.

Pour chocolate mixture into egg whites. Fold through until incorporated and no more white lumps remain - aim for 12 folds max, but ensure there are no obvious egg white patches.

Chill in fridge - Divide mixture between 4 small glasses or pots. Refrigerate for at least 6 hours, preferably overnight.

To serve, garnish with cream and chocolate shavings. Raspberries and a tiny sprig of mint for colour would also be lovely!