Ingredients: Stock, eggs.
Whip up three or four eggs, gradually add good stock to them, and keep on whisking them up until they begin to curdle. Keep the soup hot in a bain-marie.
See also: Wikipedia Cookbook.
Source: ''The Cook's Decameron: A Study In Taste, Containing Over Two Hundred Recipes For Italian Dishes'' from a project that puts out-of-copyright texts into the public domain. This is from a *very* old source, and reflects the cooking at the turn of the last century. Update as necessary.