In a heavy-bottomed pan, heat 1 liter of full-fat milk on medium flame. Keep stirring occasionally to prevent it from sticking to the bottom.
Once the milk starts boiling, reduce the flame to low and let it simmer for 20-25 minutes, stirring occasionally, until it reduces to half its original quantity.
Add 100 grams of sugar to the reduced milk and mix well. Cook for another 5 minutes, stirring continuously.
Remove the pan from the heat and let the milk mixture cool down to room temperature.
In a blender, add 200 grams of fresh or frozen blueberries and blend until smooth.
Mix the blueberry puree into the cooled milk mixture and stir well.
Pour the blueberry kulfi mixture into kulfi molds or small cups. Cover with aluminum foil or plastic wrap and insert a popsicle stick or ice cream stick in the center of each mold.
Freeze the kulfis for at least 6-8 hours or overnight until they are completely set.
To serve, gently remove the kulfis from the molds by running them under warm water for a few seconds. Enjoy the delicious blueberry kulfi!