In a heavy-bottomed pan, pour 1 liter of full-fat milk and bring it to a boil. Keep stirring occasionally to avoid burning.
Once the milk starts boiling, reduce the heat to low and let it simmer for 30-40 minutes, stirring occasionally until it reduces to half its original quantity.
Add 100 grams of sugar and 1/4 teaspoon of cardamom powder to the reduced milk. Stir well and cook for another 5-7 minutes.
In a small bowl, mix 2 tablespoons of milk with 1 tablespoon of cornflour to make a smooth paste. Add this paste to the milk mixture and cook for another 5 minutes, stirring continuously to avoid lumps.
Remove the pan from heat and let the mixture cool down to room temperature.
Once cooled, add 50 grams of chopped mixed nuts (almonds, pistachios, and cashews) to the mixture and mix well.
Pour the kulfi mixture into popsicle molds or small cups, insert a wooden stick in the center of each mold, and freeze for 6-8 hours or until completely set.
To serve, gently remove the stick kulfi from the molds by running them under warm water for a few seconds.