In a small bowl, combine the sour cream, cumin, and 1/4 teaspoon of the salt. Cover and refrigerate.
Heat the oil in a large saucepan over medium-high heat. Add the garlic and cook for 1 minute. Add the tomatoes and their juices, the pepper, and the remaining salt and bring to a simmer. Cook for 10 minutes. Add the jalapeños or hot sauce and hominy and simmer for 5 minutes. Add the shrimp and simmer until pink and cooked through, 3 to 4 minutes. Ladle the soup into bowls, top with a spoonful of the cumin cream, and sprinkle with the cilantro (if using). Serve the lime on the side.
Tip: Hominy, sometimes called posole, refers to corn kernels minus the outer hull and the germ. You can find it with the other canned vegetables or south-of-the-border ingredients at most supermarkets.