Interestingly enough, the OED dates yummy "French toast" recipes to the 17th century.

The "toasted on the dry side" version seems to come only from the 1920s.

It makes me wonder if the one-sided toast was named because that was about the only way you could make toast in a trench on the Western Front, with a knife or bayonet for a toasting-fork. (Assuming you had bread, which was something of a luxury in a forward area.)