The 2-Ingredient Addition Julia Child Used To Enrich Her Watercress Soup

Watercress isn't exactly a veggie at the forefront of most peoples' minds. Sure, you can make a mean salad with it, and watercress was even used to make a virility beer that was produced in 2018, but it's not exactly known for its star power. What it is known for is its role in a classic Julia Child recipe. That's right, we're talking about watercress soup. Often criticized for being thin and flavorless, Child brought a hearty twist to this classic by adding just two ingredients: egg yolks and cream.

Specifically, Child added two egg yolks and about a ½ cup of cream to enrich her soup. To do as Child did, just plop the yolks into a bowl, add your cream, and whisk it all together until it's homogenous. (As Child herself said in a video posted to YouTube, you always want to mix your egg yolks with something cold before adding them to a hot dish like soup as this ensures the eggs won't scramble before your eyes.) After the eggs and cream are combined, pour the watercress soup back into the mixture, stirring all the while. The end result of this process is a velvety soup with an incredibly rich taste. While the egg yolks and cream have already enriched this watercress soup, Child also added a few pats of butter prior to serving. However, this final step is not absolutely necessary. 

Thick soups are beloved the world over; just look at the popularity of chowders. However, not every soup is thick from the get-go. Thankfully, during her career, Julia Child shared many techniques for thickening soups, and not all of them called for eggs. In fact, she often thickened soups by making a roux. You can do this by combining and heating flour and fat (usually butter or milk) until they form a paste. This paste can be used to enrich just about anything from soup to gravy. In fact, utilizing a microwaved roux is a little-known hack for making a quick and delicious gumbo.

Another way to thicken watercress soup is to add a mixture of cornstarch and water to it. Whisk equal parts cornstarch and water together to form a thick liquid and gradually pour this into the soup. When heated, the starch molecules present in the cornstarch slurry will eventually burst, thickening the soup. Another way to achieve a similar result is to add straight-up boiled and mashed potatoes to the soup. This not only thickens the whole thing up but also adds an earthy flavor, making the bowl of soup heartier and more filling. (Culinary legend Jacques Pépin has a similar trick, although he uses instant mashed potato flakes to thicken his soup.)

It is important to remember that while cornstarch or mashed potatoes will thicken soup, they will not add as much flavor to it as eggs and cream do. That being said, whichever enriching method you decide to try, your watercress soup will become thicker and more satisfying. As the master herself used to say, bon appétit.