Asparagus Egg Noodle Soup (Gluten Free Option)

I list the lemon zest as optional because, though it provides added flavor, I have forgotten to add it on occasion and the soup is still delicious!

1 tablespoon olive oil
1 pound asparagus, trimmed and sliced into bite-size pieces (about two bunches or 3 cups)
1 1/2 quarts (6 cups) chicken broth, plus an extra cup or so to thin any leftovers
Zest of half a lemon, optional
3-4 ounces angel hair pasta, broken into small pieces (see notes for details and gluten free options)
3 egg yolks
1/2 teaspoon kosher salt and a few turns of the pepper mill
1/4 cup shredded Parmesan cheese

Heat the olive oil in a large pot. Sauté the asparagus over medium-high for 2-3 minutes, depending on thickness, or until crisp-tender. Remove to a plate.
Add the 6 cups of broth and the lemon zest. Increase the heat to high and bring the broth to a boil. Stir in the pasta and cook for 2 minutes. Reduce the heat to low.
In a medium bowl, beat the egg yolks. Slowly add one cup of the hot broth to the yolks, whisking as you add. Then whisk the egg mixture back into the soup pot. Whisking consistently as you pour the mixture back in will allow it to fully and smoothly incorporate into the broth.
Bring the soup back to a simmer for one minute, adding the sautéed asparagus, and salt and pepper to taste. I typically add about 1/2 teaspoon of kosher salt and 1/4 teaspoon of pepper. This may vary according to taste and what type of broth you use.
Remove soup from the heat, ladle into bowls, and garnish with the Parmesan cheese.

Use the smaller amount of pasta if you prefer a "brothier" soup, the larger amount if you like it a bit heartier.
While I started making this soup with angel hair pasta many years ago, I now often make it with rice or bean vermicelli noodles for a gluten free option. The bean vermicelli are glassier when cooked and difficult to break, so I often rough cut them with my kitchen scissors (in the pot, once cooked) to make the soup easier to eat. My kids actually love these noodles.