Soak Almond in water at least 3-4 hours in a bowl.In a separate bowl soak cashew,melon seed and poppy seeds for 3-4 hours.
Peel the almonds.Grind together almonds,cashew,melon,poppy seeds,fennel seeds,cardamom and peppercorn with little water and make a fine paste.
This paste can be made a day or two ahead and kept refrigerated.
In a bowl mix together the biscuit crumbs, sugar, and melted butter. Press onto the bottom and up the sides of a well greased 8-9 inch tart pan with removable bottom. (A spring form pan can also be used).Place in the refrigerator to set while you make the filling.
Note: If you want you can bake the base for 10 minutes at 180 degree,it is optional.
In a blender blend cheese,yoghurt,cream,saffron infused milk,sugar,gelatin mixture and rosewater until everything is well incorporated. add 1/3 cup of above thandai mixture and give one more whisk.
Pour the mixture into the biscuit base , smooth the top.Cover and refrigerate at least 5 hours or overnight.
Note: rest of the mixture can be added to cold milk and served chilled to beat the heat.