Boil the sugar and 5 tablespoons of water until the sugar dissolves, allow to cool. Remove the cardamom seeds from the capsules and crush in a mortar. Mix yoghurt and sugar syrup with a whisk.
Stir 2-4 tablespoons of water vigorously until the lassi throws small bubbles. Stir in cardamom and rose water. Put in a cool place. Decorate with rose petals.