In a heavy bottom pan, add condensed milk and whole milk and mix well. Start with 4 cups of milk. Depending on how sweet you like, you may add up to 5 to 5 ½ cups of milk. (Remember the mixture thickens on cooling)
1 can Sweetened condensed milk, 4 ½ cups Whole Milk
Bring this to a nice boil by stirring it occasionally so that it does not stick to the bottom and get burnt or browned.
Reduce the flame to low and cook for 25 to 30 minutes or until it thickens and reduces by 25 percent. Keep stirring and scraping the sides of the pan during this process, and add any milk solids back to the mixture. Scraping is what gives basundi a thick and creamy texture. If you want it thicker, then simmer it for a longer time.
Meanwhile, roast pistachios, almonds, and cashews in a pan until aromatic. Roasting is optional, but it gives additional flavor.
2 tablespoon Almonds, 2 tablespoon Cashews, 2 tablespoon Pistachios
Once the milk is thickened, add roasted nuts, raisins, saffron threads, cardamom powder, and nutmeg.
¼ teaspoon Cardamom powder, 8 strands Saffron, 2 tablespoon Raisins, Nutmeg
Stir this and simmer for another 2 minutes.
You can serve hot, warm, or cold. I recommend transferring this to a serving bowl and cooling completely. Refrigerate it for 2 hours at least before serving. The refrigeration will thicken this a little more.
Garnish it with some more nuts and saffron, and enjoy.