Avgolemono originates from Spanish Jewish people who left Spain during the Inquisition. Some of these Jewish people went to Greece, and this sauce like dish was used in favor of citrus (which was hard to come by in Europe.) Over time, the sauce was turned into a soup. It is now a widely enjoyed dish today.
This recipe makes an easy to modify version of Avgolemono. You could skip the onion (I do) but you don't have to.