M could be for Marshmallow... or even as a T for Toasted marshmallow - on a whittled stick over the embers of a fire. If you then sandwich it between biscuits (I go for digestives, unless feeling very decadent and then it would be milk chocolate hobnobs - chocolate facing in so that it melts...) it becomes a s'more (some more - as you can often want more). Traditionally a s'more is American and uses Graham crackers and includes chocolate. So this could also be S for s'more!
I've eaten way too many of these over the last 12 years.
