Soak the almonds, cashews, poppy seeds, and fennel seeds in 1 cup of water for at least 30 minutes.
Drain the nuts and seeds and grind them into a smooth paste using a blender or food processor.
In a large mixing bowl, combine the ground nut and seed mixture with milk, cardamom powder, black pepper, sugar, and saffron. Mix well until the sugar dissolves.
Chill the mixture in the refrigerator for at least 1 hour.
Serve the chilled Thandai in glasses with crushed ice.
