Brown ground beef and onion in a large Dutch oven over medium heat until beef is no longer pink and onion is limp (about 8-10 minutes). Pour off drippings. Season with salt and pepper to taste.
Stir in tomatoes, broth, water, corn and cumin.
Bring to a boil. Cover, reduce heat and simmer 10 minutes. Remove cover and stir in cilantro. Taste and adjust seasoning.
Gently press flour tortillas into six 10 ounce custard cups or microwave safe soup bowls. Microwave on HIGH for 2 minutes. Rotate and continue cooking on HIGH for 1-2 minutes. Carefully lift tortillas out and place in soup bowls.
Ladle soup over tortillas in bowls. Garnish with additional cilantro sprigs if desired.
You can substitute cooked shredded beef for the ground beef in this recipe.