Make the broth: Cover the tasajo with cold water and soak it for at least 8 hours. (There is no need to refrigerate it.) Change the water and continue soaking for another hour. Drain again and rinse under cold running water. Put the tasajo in a large, heavy pot and add about 6 quarts of water. Bring to a boil, reduce the heat and simmer, covered for 1 hour. Add the pork, beef brisket, and bay leaf, and let the three meats cook together until tender. Remove the pot from the heat and skim as much fat as possible from the broth. (If you have time, the best way is to refrigerate the broth overnight until the fat solidifies and then remove it.)
Make the Sofrito: Heat the oil in a skillet over medium heat and saute the onions and green pepper until the onions are translucent, about 3 minutes. Add the garlic and cook 2 minutes more. Add the pepper, cumin, and tomatoes and cook for another 2 minutes.
Add the sofrito to the broth and simmer, covered, while you prepare the vegetables.
Complete the Dish: Peel the malanga, boniato, name, yucca, and calabaza and cube them. Cut the corn and green plaintains into 1 1/2-inch pieces. With a knife, split the skin of each piece of green plantain and open it away from the center as if you were taking off a coat. Sprinkle the plantain pieces with the lime juice. Slit the semi-ripe and ripe plantains lengthwise and slice them crosswise into 1 1/2-inch rounds. Do not remove their skins or they will disintegrate in the stew. Add the green plantains to the simmering stew. After about 15 minutes, add the semiripe plantains. After another 15 minutes, add the ripe plantains and let them simmer for about 10 minutes.
Serve hot in soup plates or, cocido-style, with the meats, vegetables, and broth in separate dishes. (Each diner removes the skin from the semi-ripe plantains themselves).