Chop and saute the leftover half of the onion in 2 T. olive oil over medium high heat for 3-4 min
Add salt and pepper to the onion at this stage so you don't have to correct the seasoning so much at the end (maybe a teaspoon of salt)
Add chopped garlic and saute another minute or two.
Add the chicken stock and let the mixture come to a near boil
Begin to drop the meatballs into the hot broth
After all the meatballs are added, let them cook for a few minutes until the meatballs begin to rise to the surface
Turn the heat down to low and add the pasta and the spinach
Cover and let it cook for about 20 minutes, stirring occasionally to keep the pasta from sticking
Uncover and check the flavor. It will likely need more salt and pepper and I often add a teaspoon or two of honey
Beat the two egg yolks well and ladle a little of the soup into the eggs and mix well
Add the egg/soup mixture back to the soup and stir.
Serve with crusty bread, grated parmesan cheese and smooches!