Authentic Tortilla Soup

Why I Love This Recipe
This recipe comes from Pastor Tom of Tom Brown Ministries. I've made it several times, and I'm here to tell you it's the most authentic tortilla soup recipe I've found, due in large part to one tiny, but very important, secret ingredient.
Ingredients You'll Need
1 16-oz. can tomatoes, undrained
1 medium onion, chopped (I like Vidalia onions)
2 cloves garlic, minced
4 Tablespoons fresh cilantro leaves
1/2 teaspoon sugar
8 cups chicken broth
1 1/2 lbs. cooked chicken breast, chopped
2 or 3 chipotle peppers (the kind that are canned in adobo sauce), chopped
garnish: shredded Monterrey Jack cheese, sour cream, guacamole, sliced avocado, tortilla chips
Directions
Put tomatoes, onion, garlic, cilantro and sugar in blender; blend until smooth.
Pour puree into large pot, add broth, chicken and chipotle peppers.
*Add at least 1/2 teaspoon adobo sauce from can. *This is your SECRET INGREDIENT; without the adobo sauce the soup will taste flat.
Simmer soup 20 minutes.
If you want the soup spicier, add more adobo sauce 1/4 teaspoon at a time; can also add more chipotle peppers 1 at a time.
Put desired garnish in bottom of each bowl, ladle soup into bowl over garnish.