What is "tahdig"

Tahdig (, tah "bottom" + dīg "pot") is a speciality of persian cuisine consisting of crisp rice taken from the bottom of the pot in which the rice ( chelow) is cooked. It is traditionally served to guests at a meal. Ingredients commonly added to tahdig include yogurt and saffron, bread, potato and tomato. Variations of tahdig include placing thin vegetable slices at the bottom of the pot, so they crisp up instead of the rice. Common vegetables include potato, carrots, and lettuce. Iranians also apply this crisping method to spaghetti as well, providing a hardened base.