Doi is an Indian version of yoghurt that is usually made at home.
It has less water and less whey than European styles of yoghurt.
Bacteria is added to whole milk to ferment and congeal it. The resulting Doi will take on the shape of the container it was made in.
It’s used in sauces, marinades, desserts and drinks.
A more sour version is called “Tak Doi.”
Substitutes
Greek yoghurt, or plain western style yoghurt, drained well (pressed through a cheesecloth, and let set in the cheesecloth in a colander for an hour). If you are going the drained yoghurt route, be prepared to start with 4 times as much as you need, as you will only end up with about 1/4 of the volume / weight after you are finished.