Chocolate Mousse

Set the chopped chocolate and butter in a bowl over a pan of barely steaming water — the bowl should not touch the water. Stir gently and let them melt together into a single, glossy mass. Pull the bowl off the heat the moment the last shards disappear; chocolate scorches and grain the instant it overheats. Let it cool to just warm to the touch, around 40°C, before anything else goes in.

Whisk the egg yolks, vanilla, and salt together, then whisk them into the warm (not hot) chocolate in one go. The mixture will thicken and pull together into a dense, deeply shiny paste — almost like a soft ganache. Work quickly and confidently; if the chocolate is too hot the yolks will scramble, and if it sits too long it stiffens. You want a base that is supple and pourable, ready to receive air.

In a spotlessly clean, grease-free bowl, whip the egg whites until frothy, then rain in the caster sugar a spoonful at a time as you beat. Continue to a soft, glossy meringue that holds a peak which curls gently at the tip. Stop short of stiff and dry — an over-beaten meringue turns grainy and refuses to fold in smoothly, leaving white specks through the mousse.

Whip the cold cream to soft, droopy peaks — barely past pourable, what the French call 'à la chantilly molle'. It should mound but still flow when the bowl is tilted. Stop early; cream that is whipped stiff makes a heavy, buttery mousse and risks turning grainy when folded.

First whisk a third of the meringue vigorously into the chocolate base to slacken it — this sacrificial third makes the rest fold in without deflating. Then add the remaining meringue and the whipped cream together and fold with a large spatula, cutting down through the center, sweeping along the bowl, and turning over, rotating the bowl as you go. Stop the instant no streaks remain. Spoon into glasses or a serving bowl and chill at least 3 to 4 hours, or overnight, until set but still pillowy.