Instead of a burger with a side of fries, this open-face sandwich puts a burger on a slice of toast and tops it with a cheese sauce and serves it with fries; corned beef, ham, deep fried pork tenderloin, grilled or fried chicken breast or fried fish fillets can be substituted for the burger, but a great cheese sauce is deemed essential. There is a smaller "pony shoe" version and "breakfast horseshoe" made of eggs and hash brown potatoes. Although the sandwich was invented in Springfield, Illinois in 1928 of universally popular ingredients, it has not spread outside the region.