This is an audio file from KCBX FM (Central Coast Public Radio from California. The segment identifies that Americans have confused yams and sweet potatoes and more often than not, what is labeled a yam in the US is really a sweet potato.
This is said to be the origins of sweet potato casserole. Printed in 1796, it was written by Amelia Simmons who dubbed herself an American Orphan. This is touted as the first American cookbook.