Add all the ingredients to the medium jar of a grinder or food processor and grind to make a smooth powder.
You can also dry-roast almonds, cashews, peppercorns, and green cardamom over low heat for 3-4 minutes before grinding with the rest of the ingredients to further enhance the flavor of the thandai powder.
Do not over-grind; otherwise, the nuts will release their oil, and the powder will become sticky. Just pulse a few times. Then, let the mixture cool down for 5 minutes. Pulse again and keep cooling the mixture in between. Pulse until a powder is made.
Sift through a fine mesh sieve. Any coarse bits can go back in for a second grind.
Store the powder in an airtight container at room temperature for up to a week or refrigerate for up to 2 months. You can also freeze it for up to a year. A rancid or musty smell or oil seeping from the powder means the nuts have oxidized. Discard and make a fresh batch.
Video
Notes
To make Thandai using Thandai powder, heat milk in a pan over medium heat. Once the milk comes to a boil, add 1 tablespoon of Thandai masala powder per cup of milk, then cook for 2-3 minutes to let the flavors seep into the milk. Add sugar to taste, then cook for another minute to dissolve it. Refrigerate the milk for 1-2 hours or until chilled. Refrigerating is also important for the flavors to seep into the milk, so do not skip this step. Strain it using a fine-mesh strainer, a nut milk bag, or a muslin cloth. Stir in a few drops of rose water. Garnish with dried rose petals and serve chilled.Reduce the black peppercorns if you prefer a milder kick.To make this traditional drink vegan, you can use almond milk instead of dairy milk.