In a large heatproof bowl, whisk together the egg, egg yolks, and sugar until just combined. Meanwhile, scald the cream in a medium saucepan. Off the heat, add the chocolate and espresso and whisk until the chocolate is melted. Slowly whisk the cream mixture into the egg mixture, then whisk in the coffee liqueur and vanilla. Transfer to a large measuring cup and pour into the prepared ramekins until full.