Melt the chocolate. Place the chopped chocolate in a heatproof bowl set over a pot of barely simmering water (make sure the bowl doesn’t touch the water). Stir until smooth, then remove from heat and let it cool to lukewarm. It should be fluid but not hot.

Whip the cream. In a chilled bowl, beat the heavy cream and vanilla to soft peaks. Do not overwhip. Cover and refrigerate while you prepare the rest.

Separate and prepare eggs. Place egg whites in one clean bowl and yolks in another. Add a pinch of salt to the whites. To the yolks, add half the sugar (about 2 tablespoons) and whisk until slightly thickened and lighter in color.

Combine yolks and chocolate. Slowly whisk the lukewarm melted chocolate into the yolk mixture until smooth and glossy. If it starts to seize or look grainy, the chocolate was too cool—gently warm the bowl over steam and whisk again.

Beat the egg whites. With clean beaters, whip the whites on medium speed until foamy, then gradually add the remaining sugar. Continue beating to medium-soft peaks—glossy and fluffy, with tips that gently fold over.

Lighten the chocolate base. Fold one big spoonful of whipped cream into the chocolate-yolk mixture to loosen it. Use a gentle, sweeping motion with a spatula.

Fold in the egg whites. Add the whipped egg whites in two additions, folding carefully to keep as much air as possible. Stop as soon as no streaks remain.

Finish with the cream. Fold in the remaining whipped cream just until uniform. The mixture should be airy and soft.

Portion and chill. Spoon into small glasses, ramekins, or one serving bowl. Cover and chill for at least 2 hours, or up to 24 hours, until set and silky.

Serve. Top with a dollop of whipped cream, a few chocolate shavings, or berries. Serve cold with small spoons.