This is a healthy and easy to make broccoli soup.
In a medium to a large stockpot, (I used a large saucepan) melt 2 Tbs. of butter over medium heat and add the onion, celery, and garlic. Saute until the onion becomes clear and the garlic fragrant (about 5-6 minutes).
Add the broccoli and saute for a couple of minutes. Add the chicken stock and simmer for 10 minutes.
With an immersion blender, blend the mixture for about 10 seconds to break up the broccoli.
Add the flour, butter, cornstarch, and milk. Stir. Simmer over medium heat for 10 minutes. This will thicken the mixture. You may want to puree with the immersion blender a little bit longer if you would like the soup thinner in texture. I kept mine a little thicker.
Pour into bowls and add the cracked walnuts to the top along with a tsp. of sour cream (optional).
Add cracked pepper and sea salt to taste.