1 tomato, seeded & diced

1/2 teaspoon dried epazote

1/2 teaspoon cumin

1/4 cup dry sherry

salt

Freshly ground black pepper

1 cup ham, diced small - optional

Rinse the beans well - you don't want grit or dust in your finished dish.  Also give them a quick look-over to make sure there aren't any cunningly black little rocks in there - depends where you get your beans, but sometimes you find little tiny stones in dried beans.

Cover rinsed beans with fresh water, up to about two inches above the beans. Bring to a gentle simmer and cook until tender, stirring occasionally. This can take as little as an hour or as long as two or two and a half hours, depending on how old your beans are. Play it by ear, but don't let the beans boil hard, or they will split and turn quite mushy.  Most of the time, I find that dried black beans are ready in just one hour. Once the beans are tender, you can add a little salt - if you are using stock, make sure you don't over-salt at this stage.

Note that if you have hard water (or beans of dubious age), a scant pinch of baking soda added to the water when you begin to cook the beans will help soften them more quickly.  You can make the beans a day ahead, and then proceed from this point when you want to serve them.

Remove two thirds of the beans to a blender or food processor and puree.*

In a medium frying pan, heat the oil and saute the onion, garlic, and pequin chiles until the onion is soft.  Add the tomato, epazote and cumin and stir until well blended.  Add the onion mixture to the black bean puree along with the extra water (or stock) and simmer for a few minutes so that the flavours mingle. Puree the mixture again until as smooth as possible.  Stir back into the cooked beans and continue to stir until the mixture thickens and becomes smooth. 

Add the diced ham and simmer gently to heat through, stirring frequently.  Remove any stems from the epazote that might have escaped the food processor.  Add the sherry and stir through.  Serve with baked tortilla-crackers.