Dissolve espresso powder in hot water.
Set it aside to cool slightly.
Whisk egg yolks and sugar in a bowl.
Heat milk in a saucepan until warm.
Slowly whisk warm milk into yolk mixture.
Return mixture to the saucepan.
Stir constantly over low heat.
Cook until it slightly thickens.
Remove from heat and stir in espresso.
Stir in vanilla and let it cool.
Sprinkle gelatin over cold water.
Let gelatin bloom for five minutes.
Stir bloomed gelatin into warm custard.
Cool the custard to room temperature.
Beat cream until soft peaks form.
Fold whipped cream into custard gently.
Spoon mousse into serving glasses.
Chill for at least four hours.
Garnish with shaved chocolate or cocoa.
Serve cold and enjoy the bliss.