This 5 minute mousse only requires 4 ingredients, and is so easy to make.
Chop the chocolate into pieces. Place in a blender or food processor, then pulse.
Heat some heavy cream and brew the espresso. Place them together with the egg yolk into the chocolate mixture. Blend and set aside.
Whip the remaining heavy cream. Fold in the chocolate.
Divide between two glasses and chill before serving.