Finely chop chocolate and place in bowl. Add 1 tsp butter. Heat cream, espresso, cinnamon and cardamom in small pot. Bring to the boil.
Pour cooked cream mixture over chopped chocolate and leave 3–4 minutes. Gently stir cream and chocolate until mixture is smooth. Cool well, best overnight.
Scoop chilled mixture into walnut sized balls, and shape between your palms. Roll each ball in cocoa powder, and chill well before serving.