Soak saffron in warm milk for 10 minutes. Set aside.
Meanwhile, combine milk + half-n-half in a large pot.
Add sugar and whisk to combine.
Stir in Thandai Powder. Whisk it well.
Stir in Rose petal jam or gulkand.
Bring the milk mixture to a boil. Keep whisking the thandai. Once the thandai comes to a full boil, take it off the flame.
Allow the Thandai to sit for a while (an hour or more) so that it can soak in all the flavors. Stir in rose water and mix it well.
Strain the mixture through a sieve. Press the leftover gritty stuff with a spoon and allow the thandai to drain through the sieve.
Pour in saffron milk that we had prepared earlier in the recipe. Mix to combine.
Cover the Thandai mix with a plastic cover. Refrigerate for 3-4 hours or overnight.
Chilled thandai is ready to be served. Give it a good stir.
Pour in glasses. Garnish with slivered almonds, saffron strands and serve chilled.