In a large pot combine the onion, garlic, celery, red pepper, and chicken stock. Simmer on medium low for 10 minutes. Add in ¾ cup beans, salt, and cumin and cook for an additional 5 minutes.
Puree the soup with an immersion blender or by transferring to a blender. Add contents back to pot. Pour in the rest of the beans.
Mix cornstarch and water together in small bowl.
Add lemon and cornstarch to the soup simmer 10 minutes to thicken.
Recipe by Supper for a Steal at http://www.supperforasteal.com/30-minute-black-bean-soup-for-sundaysupper/