Heat the milk in a heavy bottomed non-stick pan over medium heat.
Once it comes to a boil, let it simmer and reduce on medium-low flame. Keep stirring with a wide spatula after every 3-4 minutes.
Keep stirring with scraping the bottom of the pan as well as the sides of the pan. As you cook, milk reduces and becomes grainy.
After 40 minutes, it will become slightly thick and more grainy. At this stage, you need to stir and scrape sides continuously.
Continue to stir and cook till it becomes solid or dense like halwa. You will feel that it will take little effort for stirring.
At this time, turn off the heat.
Remove it to another bowl and let it cool completely. As it cools, khoya will thicken and harden.