Ultimate Chocolate Mousse

Separate eggs while cold, placing whites in a large bowl and yolks in a small bowl. Let whites come to room temperature for 15 minutes.

Melt chocolate and butter in a microwave-safe bowl in 30-second bursts, stirring until smooth. Let cool to about 40°C (104°F).

Whip heavy cream until stiff peaks form, glossy but not grainy.

Beat egg whites with sugar gradually until firm peaks form.

Whisk yolks, fold into whipped cream with up to 8 gentle folds. Add melted chocolate and fold again lightly.

Lighten chocolate mixture with 1/4 of the beaten whites, then fold in the rest gently until no white streaks remain.

Divide mousse into 4 glasses or ramekins, cover with plastic wrap, and chill at least 6 hours or overnight.