Whisk 1 cup whole milk or unsweetened nut milk of choice, 2 Tbsp. Thandai Masala, and 2 tsp. sugar in a small saucepan to combine, then bring to a boil over medium heat, whisking occasionally. Transfer thandai to a blender, if desired, and blend until smooth.
If serving cold, let cool slightly, then pour into an airtight container. Cover and chill until cold, at least 2 hours. Pour into an ice-filled glass and top with dried rose petals and/or saffron threads if desired. Do ahead: Thandai can be made 2 days ahead. Keep chilled.
