I doubt you've had a shrimp bisque like this lately. Welcome to the Great Southwest! We rarely get fresh seafood out here, but have certainly learned to make do (or better!) with what we can get. This wonderful bisque is warm and hearty and full of those lovely Southwestern flavors. I mention in the ingredients that home-ground cumin and coriander are better, even if they are a few months old. Oh, and don't let the amount of chili powder scare you, because there is plenty of dairy there to mitigate most of the heat.
In a 3 1/2 quart (or a little larger) saucepan or Dutch oven over medium-high heat, heat the oil until it is shimmering. Sauté the onion until it is tender. Add the garlic and sauté for 1 minute longer. Stir in the flour until it is blended. Stir in the broth, cream, chili powder, cumin and coriander and bring them to a boil. Reduce the heat, cover and simmer for 5 minutes.
Add the shrimp to the soup and simmer them until the shrimp turn pink, about 5 minutes longer. Gradually stir 1 cup of the hot soup into the sour cream. Gently return that mixture back to the pan, stirring constantly. Heat it through, but do not let it boil.
If desired, garnish the servings with cilantro, avocado and additional shrimp.