Brother John rang Mum the other day - question, did we put sugar on lettuce when we were kids? In short, the answer is YES! And boy, did it make lettuce taste yummy. As well as putting sugar on lettuce on a salad plate we also used to sprinkle the sugar on the lettuce leaf and roll it up and eat it in our fingers. This writer obviously has similar memories - but I'd question her assumption that sugar on lettuce was her mother's invention.
This writer is one of many I discovered on the net who has similar memories, although most seem to be of a traditional sandwich with two slices of bread - we used one slice and rolled it up. But it had to be fresh white bread.