Terracotta bowls are traditionally used to set mishti doi and their porousness helps thicken the dahi or yogurt nicely. But I wouldn't use a terracotta ramekin or bowl inside an Instant Pot unless the product specifically says it is oven-safe. If you are not using an Instant Pot, however, and plan to set the yogurt in a warm spot in your home, you can definitely use terracotta or clay bowls.