Tie the yogurt in a piece of muslin and hang it overnight over a bowl, in a refrigerator, to drain.
Transfer the drained yogurt into a bowl. Add the sugar substitute and mix well.
Soak the saffron in warm milk, cool and add to the yogurt mixture. Mix well.
Add the nutmeg powder and cardamom powder; mix well and chill in the refrigerator.
Serve chilled, decorated with the almonds and pistachios.