Turn me over I am done on this side

St Lawrence, patron saint of comics, is noted to have said "Turn me over I am done on this side" when being roasted alive. An alternative origin for "done to a turn"?

Not really. In the days when food was regularly roasted on spits which had to be turned continually by hand, "done to a turn" had an meaning obvious to everyone, viz. "turned on the spit just the right number of times, neither too many nor too few". Whoever invented the story about St Lawrence was clearly referencing this kind of cooking, not the other way about. (VSD)