Now, Bean, would I pull anyone's leg?
Actually®, it's just another quaint Southernism... looky here, according to the AHD:

e. Chiefly Southern U.S. The round flat cover over the hole on the top of a wood-burning stove.

http://www.bartleby.com/61/75/E0307500.html

We've just extended it to modern cooking equipment, I reckon.