Blend 1 can of black beans and half of the chicken broth in a blender until smooth.

In a large saucepan, cook and stir chopped onion, minced garlic, and ground cumin in hot oil over medium heat for 3 minutes.

Add the blended bean puree to the saucepan and mix well.

Add the second can of black beans and the remaining chicken broth to the blender and blend until smooth.

Add the second blended mixture to the saucepan with the remaining can of black beans and salsa. Mix well.

Bring the soup to a boil over medium-high heat, then reduce the heat to low and simmer for 15 minutes, stirring occasionally.

Serve the soup topped with sour cream.