Place the butter in a big pot over low warmth and soften. Add the carrots, celery, onion, zucchini and garlic to the pot. Stir after which put the lid on the pot and let sweat for half-hour.
Add the hen breasts, broth, salt and pepper and produce to a boil over excessive warmth. Scale back warmth to medium-low and proceed to simmer till hen is cooked by way of, about 8 minutes. Utilizing a pair of tongs, take away the hen and place on a chopping board. Reduce the hen into bite-size items after which add again to the broth combination.
In a small bowl, whisk collectively the egg yolks and lemon juice. Slowly add 1/2 cup of the new liquid to the egg yolks whereas whisking continuously. Then, slowly add the yolk combination to the soup whereas whisking continuously.
Add the parsley, season with further sea salt and pepper if wanted, and serve.
