In a heatproof bowl, melt the chocolate over a double boiler or in the microwave, stirring until smooth. Set aside to cool slightly.
- In a saucepan, whisk together the egg yolks, sugar, and a splash (about 2 tbsp) of cream over low heat until the mixture thickens slightly. Do not boil.
- Stir in the espresso powder or brewed coffee and vanilla extract.
- Slowly mix the melted chocolate into the egg mixture, stirring until smooth and well combined. Let it cool to room temperature.
- In a separate bowl, whip the remaining heavy cream with a pinch of salt until stiff peaks form.
- Gently fold the whipped cream into the cooled chocolate-coffee mixture in batches until fully incorporated and smooth.
- Spoon into serving dishes and chill for at least 2 hours before serving.
- Garnish with shaved chocolate or a dusting of cocoa powder if desired.