Soak all the ingredients except sugar and milk in warm water for an hour.
Add the soaked ingredients to the blender along with sugar. Use about 1/2 cup of milk to aid with the grinding, if needed.
Grind them to a fine paste.
To make Thandai, stir in 4 tablespoons of this paste to a cup of cold milk. Mix well. Serve it with ice.
Notes
The awesome part of this recipe is it is very adaptable. For instance, you can reduce the amount of fennel if you don't like the flavor or skip using cinnamon stick altogether.The quantity of most of the nuts and spices can be tailored..but here's the thing - if you don't have rose petals and saffron handy, get them if you can. The drink won't taste as authentic without them.