Soak almonds, cashewnuts, pistachios, watermelon seeds, fennel seeds, poppy seeds, black peppercorns in a bowl of water, for 4 to 5 hours.
After 5 hours, drain the water and grind all the ingredients to a fine paste. This is the thandai masala.
In a bowl, take 2 tbsp warm milk.
Add a big pinch of saffron to it and keep it aside for an hour.
Heat the milk in a thick bottomed pan.
When the milk starts boiling, add sugar.
Keep stirring till the sugar dissolves.
Add the thandai masala, and keep mixing till the masala blends well with the milk.
Add the saffron milk mixture, cardamom powder and give a good mix. Turn off the flame.
Allow the thandai to cool completely.
Refrigerate and serve chilled.
While serving, garnish the thandai with almond, pistachio slivers and dried rose petals.