Preheat oven to 275º
Place 6 ramekins in a large roasting pan. (Ramekins must lay completely flat.)
In a large, heatproof bowl, whisk egg, egg yolk, and sugar until just combined.
In a medium saucepan, scald the cream.
Remove from heat.
Add the chocolate and espresso and whisk until the chocolate is melted.
Slowly whisk the cream mixture into the egg mixture.
Whisk in vanilla.
Pour into the ramekins.
Pour hot tap water into pan around the ramekins, until water comes halfway up the ramekins. Do not splash water into the ramekins.
Bake 40 to 50 minutes, until the custard is set on the edges, but a little jiggly in the middle.
Remove from water bath and cool to room temperature.
Refrigerate until firm.
Optionally, spread 1 tablespoon of sugar evenly on top of each custard. Caramelize sugar with a kitchen blowtorch or carefully broil in oven. Let sugar reharden before serving.