Rinse black beans in colander then soak in water in large bowl overnight, or 8-10 hours.
After soaking, rinse beans again in colander.
Place beans in slow cooker, along with chopped onion, carrots, bell pepper, garlic, jalapenos, tomatoes, cumin, cayenne pepper, salt, vegetable broth, and water.
Turn slow cooker on high and cook for 6 hours.
Using an immersion blender, pulse soup 5-6 times until desired consistency.
If you don't have an immersion blender, you can remove about 2 cups of the soup and puree in blender, then return to slow cooker.
Stir in cilantro, and season with salt and pepper, to taste.
Serve topped with sour cream or Greek yogurt.
Enjoy!