Dried and semidried shrimp, moist and orangey in color, form an important part of Lenten food throughout Mexico. This is a dish from the mountain state of Oaxaca, where fresh fish is hard to come by.
Bring the beans to the boil in 8 cups / 2 liters water in a roomy pot, skim off any gray foam that rises, add the garlic, onion, and a little salt, and simmer gently for about 3 hours, till perfectly soft. Don’t let it come off a boil. If you need to add water, make sure it is boiling.
Meanwhile, put the dried shrimp to soak in a little warm water for 10 minute