Add some sugar and agar to the milk, then boil it and let it cool.

This method can also be used to make jelly. My wife used to make jelly with agar and peach meat, and it was delicious to put it in a big bowl and ice it.

It is really nonsense that milk is cooked and cooled to become solid. In the past, milk was suspended, and some solids might be produced when it was cooked. But now milk is made of high-tech molecules, and it is all colloid. It seems really impossible to treat it as a solid. We know that protein will become a solid at 70 degrees, but this is irreversible. Like an egg, it becomes solid when cooked. It can also be seen that there is not enough protein in milk.