Prepare the Coffee Mousse
Whip heavy cream, sugar, espresso powder, and vanilla until soft peaks form.
Refrigerate while preparing ganache.
Make the Dark Chocolate Ganache
Heat cream in a saucepan until warm (don’t boil).
Pour over chopped chocolate and let sit for a minute.
Stir until smooth, then mix in butter.
Assemble the Dessert
Spoon mousse into serving glasses.
Pour ganache over the mousse.
Chill for at least 30 minutes.
Serve cold, preferably with an attitude of sophistication.