Drain the rice and spread it out on a clean kitchen towel. Cover with another towel and gently pat dry to absorb any excess moisture.
Transfer to a blender and pulse several times until it reaches a coarse, semolina-like texture.
Cook the Phirni
While the rice is soaking, rinse a heavy-bottomed pot with water and leave a spoonful of water in it (this prevents milk from scorching).
Pour in the milk and cook on medium heat for 15 minutes, stirring frequently.
Grind the saffron strands into a fine powder using a mortar and pestle. Reserve.
Stir in the ground rice and cook for 10 to 15 minutes, stirring frequently and scraping the sides to prevent sticking.
Stir in sugar, saffron and Thandai Masala and cook for additional 10 minutes, ensuring the mixture thickens to a creamy consistency. The Phirni will continue to thicken further as it cools down so make sure not to overcook it.
Chill, Garnish and Serve
Once the Phirni has thickened, let it cool to room temperature.
Cover and refrigerate overnight for the best texture and enhanced flavors. If short on time, divide into individual serving bowls and chill for at least 30 minutes to help it set faster.
Garnish with sliced pistachios and dried rose petals.