Rinse black beans and soak overnight with 1 teaspoon of salt and halved red bell pepper.

In a 6-quart stewpan, bring soaked beans, soaking water, and red bell pepper to a boil.

Simmer until beans are tender (really tender).

Heat vegetable oil in a deep frying pan.

Saute sliced onions, minced garlic, and seeded, halved serrano chiles until softened.

Remove 2 1/2 cups of bean broth from the stewpan and add to the frying pan with the sauteed vegetables.

Simmer the mixture for 10 minutes.

Strain the onions, garlic, and hot peppers from the broth and discard them.

Remove the red bell pepper from the stewpan and discard it.

Add the seasoned broth from the frying pan back to the soup pot.

Add the crumbled Mexican chocolate, bay leaves, ground cumin, sugar, 3 teaspoons of salt, and black pepper to the soup pot.

Simmer the soup for 2 1/2 hours, or until it thickens.

If the soup becomes too thick, add water to adjust the consistency.

Stir in the white wine vinegar and olive oil just before serving.