Add 300gms of sugar to the milk and put to boil on Medium heat for at least 45mins and beat the milk constantly while boiling.
See that the milk is reduced to almost 40 % and becomes thick and light brown in color.
Place the remaining 200gms of sugar in heavy bottom vessel with 50ml of water and melt on low heat. Allow the sugar mixture to turn dark brown in colour. Gradually add this sugar mixture to the boiled milk and boil again for 15 minutes.
Take it off the flame and beat constantly with a jar till the mixture becomes luke warm.
Transfer the mixture into the Earthen Pot.
Mix the Yogurt into the mixture after 5 min.
Cover and allow to set for 8 to 12 hours at a warm place, do not open or move the pot during this period.
Uncover and Store in a refrigerator, Serve Chilled.