Slice the pumpkin in the size you like. Wash them well and clean their seeds and chop them big. Put them in a large pot by adding sugar between each line.
Put its lid on and wait it overnight, at least 6 hours. During this time, pumpkin pieces release their juice, so we don’t need to add extra water while boiling it.
Put the pot on the medium heat and cook the pumpkin pieces until they get soft. Bring it to boil a few times without the lid on. In this way, the syrup of it will be denser. Then let it cool in the same pot.
After they are cold enough, wait it in refrigerator for a while. Then serve it cold.
If you like, you can garnish it with some pistachio, walnut or coconut.