4 large egg yolks
1/4 cup sugar
Pinch of salt
2 tablespoons unsweetened cocoa powder
2 ounces bittersweet chocolate
3/4 cup heavy cream
STEP 1
Finely chop chocolate; reserve. In a double boiler, whisk yolks, sugar, and salt until sugar has dissolved and mixture is warm to the touch, 2 to 3 minutes. Off heat, quickly whisk in chopped chocolate until melted and cocoa until smooth (mixture will be thick). Cool to room temperature.
STEP 2
In a medium bowl, whip cream until soft peaks form. Whisk half of whipped cream into room-temperature chocolate mixture. Gently fold in remaining whipped cream with a rubber spatula. Divide mousse among four serving dishes. Chill at least 2 hours and up to 1 day.
STEP 3
Remove mousse from refrigerator 15 minutes before serving. Garnish with shaved chocolate.