Add onions and cook, stirring, until onions are softened, about 5 minutes.
Add the garlic and cumin, cook another minute.
Add beans, broth, water, salt/pepper and cayenne.
Bring to a boil then reduce heat and simmer for 10-15 minutes.
Remove from heat and let cool 5 minutes.
Either use an immersion blender, regular blender or food processor and blend until smooth.
Add cilantro, and serve.
Notes
Additions:Add some sour cream swirled into the top before serving (not for vegans)A little chili powder will amp up the heat (see below for how to REALLY amp it up!Storage/Freezing:Allow to cool completely then store in sealed containers in the refrigerator for up to 4 days. Freeze up to 3 months. To reheat, microwave until fully heated through.How to make Spicy Black Bean Soup:Bump up the cayenne, or add red pepper flakes with the spices.Add a can of chopped green chilies when you add the black beans.Add hot sauce to your bowl at serving time.