Melt the butter in a medium sauce pan over medium heat. Add onions, jalapenos, and a healthy pinch of salt. Stir to coat in butter, then cook for ten minutes.
Stir in garlic and seasonings, and cook for three minutes.
Stir in the drained/rinsed black beans and water, then cover the pot with a lid. Allow the beans to simmer for ten minutes, until softened.
Uncover the pot, and turn the heat down to low. Once the beans are not actively bubbling, use a large spoon to stir the beans, and gently smash the beans against the side of the pot. Continue smashing until they form a creamy, thick texture.
Stir in the sour cream and hot sauce. Carefully taste, and season with more salt if needed.
Serve hot, and top with crumbled cotija cheese and cilantro, if desired!