Warm the cream. Put 4 chocolate mint bars aside for decorating. Add the remaining bars to the cream and bring to the boil while stirring. Pour into a bowl and chill overnight. The next day, whisk the cream with the whisk of the hand mixer until stiff, while allowing the cream hardener to trickle in.
Finally, briefly stir in the yoghurt. Place 3 sponge fingers in each glass and spread the cream in the glasses. Halve the remaining chocolate mint bars and decorate the cream with them. Keep cool until serving, then decorate with a mint leaf