Douglas Harper's Etymology Dictionary
johnny-cake
1739, American English, of unknown origin, perhaps from Shawnee cake, from the Indian tribe. Folk etymology since 1775, however, connects it to journey cake.
Usage examples of "johnny-cake".
Perhaps tomorrow I'll be the one who least minds suiting up and going outside to get the water, and you'll be in the mood to turn out some johnny-cake or porridge while others feed the stoves and chickens.