Chicken broth thickened with rice and a froth of egg and lemon, tempered in so it turns silky rather than scrambled.
What makes it avgolemono
Eggs beaten with lemon juice until frothy.
Hot broth whisked in slowly to temper them.
Never boiled afterwards, or it curdles.
Where it comes from
Avgolemono is both a sauce and a soup: egg and lemon beaten together and thickened with hot broth. Similar egg-and-lemon sauces are made by Sephardic Jewish cooks and across the Balkans and Turkey.
As soup, with chicken and rice, it's what's made for someone unwell; at Easter it finishes magiritsa, the soup that breaks the Lenten fast.
How it varies
Magiritsa
The Easter soup of lamb offal and herbs, finished with avgolemono.