In a thick bottom pan or nonstick pan, bring the milk to boil.
Continue boiling till the milk reduces to half. This takes about 20 to 30 mins.
Keep stirring regularly to avoid them to form or the bottom from getting burnt.
When the milk is reduced to half, slowly add the lemon juice and stir well.
Keep stirring till you get fine granules of the curdled milk.
Slowing add sugar in batches and continue cooking.
When the whole milk turns into a mass, add ghee and continue cooking further when you see the milk solids leave the sides.
I have captured each stage with pictures, you can refer that for more clarity.
Have a greased loaf tin ready, I used a cake pan with a lid.
Transfer the halwa into the tin and cover with lid.
Now, wrap the tin with a thick turkey towel to prevent losing out on the heat.
This way, you will sugar caramelized in the center giving you the characteristic white and brown colour in the center.