Method

Heat milk at medium flame setting in a heavy bottom non stick pan.
When the milk comes to a boil turn the gas down to the lowest flame setting and let it simmer and reduce in quantity.
Keep stirring after every 2 minutes so that the mixture doesn't stick to the bottom of the pan and doesn't burn.
Use a wider spatula so that it will cover the more area of the bottom pan while stirring and it will make your job easier.
Keep stirring with all the while the bottom of the pan and the sides of the pan.
Milk will reduce and turn grainy. After approx 40-50 minutes the milk will become more grainy.
Keep stirring the bottom and the sides of the pan continuously.
keep stirring and cooking till it becomes solid or dense like halwa.
After approx 1.15 hours of stirring and cooking when the milk becomes solid turn off the gas.
Remove it from the hot pan and put it in another bowl till it cools completely down to room temperature.
At the time of cooling it will thicken and harden more.