The Flash Dictionary,1821
I have seen a romance author or two reference this, and honestly I think at the time I probably thought they meant a hot flannel literally. Unless they implied it was a drink. Nevertheless, its useful to know that a Regency lady or gent may have wanted a hot flannel, particularly in the winter, to warm up with. Kind of like a spiked eggnog, this also was known in Colonial America as a Flip and apparently popular with the Coach drivers.
I have also seen recipes that replace the gin with rum, which would probably make it a bit more egg-noggy (or at least less junipery).
