Step 1

In a small saucepan, saute the onion in oil until tender. Add the garlic and cook 1 minute longer. Stir in the flour until blended. Editor's Tip: A roux sounds fancy and French, but it's simply a paste of flour and fat, which makes a flavorful, thick base for a soup.

Step 2

Stir in the water, cream, chili powder, bouillon, cumin and coriander. Bring to a boil, then reduce the heat. Cover and simmer for 5 minutes.

Step 3

Cut the shrimp into bite-size pieces. Add them to the soup. Simmer for 5 minutes longer, or until the shrimp turn pink.

Step 4

Remove about 1/2 cup of soup from the pot and gently whisk it into the sour cream. Return all to the pan, stirring constantly. Heat through, but do not boil. Remove from heat. Editor's Tip: Boiling the sour cream will make it curdle, so be extra careful not to let the soup get too hot.

Step 5

If desired, garnish with cilantro, avocado and additional shrimp.