The uses of beans in Mexican cooking are immense. Although you can buy them already made, if you make them at home they have a much nicer flavor and you will give your kitchen an irresistible smell. You can make a lot of them and refrigerate a batch which should last in the refrigerator for about 4 to 5 days. You can freeze another batch which will last for months.
I will give you two tips, included in the recipe below, if you make them at home:
1. Don't add the salt in the beginning or it will toughen the beans. Add it at least after an hour of cooking when the beans are already a bit soft.
2. You don't need to soak them the night before cooking. Yes, that helps to reduce the cooking time, but it is not necessary. If you do soak them, don't soak them more than 12 to 14 hours, because they may begin to ferment and you will finish with a Chinese rather than Mexican tasting dish.
I like making them with either Black beans, traditional in the South of Mexico, Peruvian beans, which are more used in the Central part of Mexico, or with Pinto beans which are more customary in the North. The latter ones have a creamier feel and more subtle flavor.
Traditionally Frijoles de la Olla are cooked in an earthenware pot. It does impart a special Pueblo style flavor.
Many cooks in Mexican kitchens make them in pressure cookers, as it cuts the time almost in half, but I am a bit weary of them, as I have seen one too many explode!! Plus, cooking beans only requires you to be home for a certain amount of time, you don't need to do anything but peek in every once in a while to make sure that there is still enough liquid.
I cook mine sometimes in an old earthenware pot and sometimes in a normal large cooking pot. They both work very well.
FRIJOLES DE OLLA
Makes about 5 cups beans and 2 cups cooking broth
1 pound or about 2 1/4 cups, Pinto, Peruvian or Black beans
1/2 white onion, about 1/2 pound, peeled of outer skin
10 cups of water, may add more if necessary
1 tablespoon kosher or sea salt, or to taste
Rinse the beans in cold water and drain. Place them in a big heavy pot and cover with enough water to come up to at least 3" above the top of beans, about 10 cups of water. Incorporate the onion and bring to a boil. Let the beans simmer, partially covered, for about 1 1/2 hours, until the beans are soft and then add the salt. Don't add the salt in the beginning or it will toughen the beans.
Let them continue simmering, for about another 15 minutes, or until the beans are so soft they come apart if you hold one between your fingers, and the broth has thickened to a soupy consistency. If the beans are not yet soft and the broth is drying out, add more water. Before eating, remove the cooked onion with a slotted spoon.