There are two meanings for “upper crust.” It may be the topmost layer of a loaf of bread, a pastry dish, or other food item with a hardened coating, or the Earth’s surface. But we’re most used to using the phrase to refer to the wealthiest members of society, who also wield the greatest political power.
One tall tale suggested that a loaf of bread was divided according to status. Lowly workers got the burnt bottom of the loaf, the family got the middle, and guests got the top, or “upper crust.” While the phrase appeared in reference to the Earth’s surface, and to bread and pies for several centuries, it wasn’t until the 1800s that it was used to mean upper-class people.
Also in the 1800s, “upper crust” appears as a slang term for the human head or a hat. Most likely it’s simply the idea of the upper crust being the “top” that made it a metaphor for the aristocracy. Here’s how Thomas Chandler Haliburton put it in his 1838 The Clockmaker; or the sayings and doings of Samuel Slick of Slickville: “It was none o’ your skim-milk parties, but superfine uppercrust real jam.”
The earliest example of the term with the meaning of the aristocracy is in Slang: A Dictionary of the Turf, by John Badcock, 1823: “Upper-crust — one who lords it over others, is Mister Upper-crust.” The term was still being used to refer to a person’s head or hat when the “aristocracy” meaning was coined.
Some people think that the top crust of a loaf of bread is the tastiest and best, but I prefer the soft squishy middle. Spread with honey, of course.