Put the chocolate and milk in a heatproof bowl and melt over a saucepan of gently simmering water. To release the cardamom seeds, crush the pods using a pestle and mortar. Discard the pods and crush the seeds finely.
Place the cardamom pods and tofu in a food processor with half of the sugar, and blend well to a smooth paste. Turn the mixture into a large bowl.
Whisk the egg white in a thoroughly clean bowl, until it forms peaks. Gradually whisk in the remaining sugar.
Beat the melted chocolate mixture into the tofu until completely combined. Using a large metal spoon, fold in the egg white. Spoon the mousse into small coffee cups or glasses and chill for at least 1 hour. Serve topped with spoonfuls of crème fraîche or yogurt and a light dusting of cocoa powder.