Huitlacoche is a fungus that grows on the outside of ears of corn. This typically Hispanic ingredient is collected and prepared with onions and chiles and served with quesadillas, soup and other traditional foods.
This ingredient may be difficult to find locally. Most commonly you'll find it in cans in very well stocked Mexican markets. Many Mexican markets don't even stock it because it tends to be high-priced. Select a reliable brand like Goya. You can find it online at: Goya Huitlacoche at Amazon.com