These rich little cups of chocolate are the perfect ending to a meal.
I like to garnish each cup with candied orange peel and chocolate-covered espresso beans to give you an idea of the flavors of the mousse. You could also try a dollop of whipped cream and chocolate shavings, too.
You can make the mousse ahead of time and chill it in the serving cups until you're ready for dessert.
In 1 bowl,* add the chocolate, butter, and espresso powder. Slowly melt over a saucepan of simmering water. Do not let the bowl touch the water because the chocolate will burn. Remove from heat and allow to cool for a few minutes. One at a time, whisk in the eggs yolks and orange zest. Keep in the refrigerator until needed.
In the next bowl, whip the 2 egg whites and cream of tartar until foamy. Slowly add 2 tablespoons of the sugar until stiff, glossy peaks form.
In the cold bowl, add the heavy cream, vanilla, and the remainder of the sugar. Whip until soft peaks form.
In the refrigerated chocolate bowl, gently fold in 1/3 of the egg white mixture. Continue to fold in the egg whites to lighten the chocolate. Repeat with the heavy whipping cream. Remember do NOT stir; fold in the egg whites and the heavy cream so as to not deflate the whipped whites and cream.
Remove your chilled serving bowls. Spoon the mousse into each glass and top with chocolate-covered espresso beans (I like to smash some and leave some whole) and candied orange peel. Cover and refrigerate or serve right away.