Cheerio! A Book of Punches and Cocktails by Charles (1928, p.30)

1 whole eggegg — raw eggbase
1 glassboiling milk other
1 small lumpButter — Big as the end of your fingernail.other
1 spoonfulsugar sweetener
  1. Beat a whole raw egg into a glass of boiling milk.
  2. Add the sugar and a small lump of butter, stir well, and serve hot.

Ice: None

See also: Egg Nog, Milk and Seltzer

Source frames it as healthy and refreshing for growing children.