Add the almonds, pistachios, cashews, pumpkin seeds, cardamom pods, fennel seeds, poppy seeds, black peppercorns, dried rose petals, and nutmeg to a blender or spice grinder. Pulse several times to break down some of the larger pieces, and then run the blender until everything is a fine powder. Do not over-grind the spices into a paste.
Thandai
Pour the milk into a large saucepan. Turn the heat to a medium low flame. Once the milk comes to a simmer, remove about half a cup. Transfer the half cup of milk to a small bowl. Crush the saffron strands between your fingers and into the bowl. Allow the saffron to bloom for 10-15 minutes.
Add the sugar and a third of the thandai masala into the saucepan with the rest of the milk. Simmer the milk for 10-15 minutes, stirring frequently to prevent the milk from scalding.
Remove the milk from heat and add the saffron milk back in. Pour in the rosewater. Cover the saucepan with a lid and allow the thandai to steep for a minimum of an hour.
After an hour, strain the thandai into a pitcher and store it in the fridge for two hours, but preferably overnight.
Serve thandai chilled with slivers of almonds or pistachios, and additional dried rose petals.
Video
Notes
Store the thandai masala in an airtight container for up to a week at room temperature or a month in the fridge.
Store the thandai in the fridge in a pitcher for up to a week.