Is Pesto A Mother Sauce?

Short answer
No, the five mother sauces are all based on classical French cuisine. However, that hasn't stopped people from trying to get pesto recognised as a "modern mother sauce."

Long answer
"Mother sauce" is a term coined by the legendary chef Auguste Escoffier, who built on the work of Marie-Antoine Carême. It describes five sauces from classical French cuisine: béchamel, tomato, hollandaise, velouté, and espagnole. Each mother sauce is the foundation for a family of 'daughter' sauces. For example, béchamel is the "mother" of mornay, soubise, and several other sauces.

Over the years, various chefs have attempted to increase the number of mother sauces to seven, adding demi-glace and mayonnaise to the line-up. Pesto has never been considered a mother sauce, although gourmets are keen to define it as one of the "modern mother sauces" alongside sauces like tahini, salsa, chimichurri, and chilli sauce.

The author Leslie Lennox has perhaps done more than anyone to campaign for pesto to be given the same status as the five French sauces with her book, "Pesto: The Modern Mother Sauce: More Than 90 Inventive Recipes That Start with Homemade Pestos." Some chefs argue that because four of the five accepted mother sauces (hollandaise being the exception) are all based on a roux (butter, flour, and milk), the list is entirely out of step with today's eating preferences and deserves to be banished to the history books.