Prepare salsa: Heat the oil in a saucepan over moderate heat. Add the onion and saute until soft, about 5 minutes. Add the garlic, jalapeno and salt and saute for 1 minute longer. Add the tomatoes with their juices and reduce the heat to low. Cook the tomatoes, stirring occasionally, until soft and juices have reduced by half, about 10 to 15 minutes. Adjust seasonings with salt, pepper and sugar to taste. Transfer the tomato mixture to a blender and puree until smooth. Set aside.
Prepare cabbage rolls: Bring a large pot of salted water to a boil. Core the cabbage and drop it into the boiling water. Boil the cabbage until the leaves loosen and come off easily, using tongs to separate the leaves. Immerse the leaves in cold water, then drain completely on paper towels.
Heat the oil in a large saute pan over moderate heat. Add the onion and saute until soft, about 5 minutes. Add the garlic, cumin and oregano, and saute 1 minute longer. Remove from heat and let cool.
In a bowl, combine the pork, beef, cooled onion, egg, bread crumbs, salt and pepper. Using your hands, mix well and divide into 12 portions.
Preheat the oven to 350 degrees F. Prepare the cabbage leaves by cutting out the tough part of the central stem from the lower part of each leaf. Spread each leaf with a portion of the filling and roll into a cylinder, enclosing the filling completely. (You may need to overlap a few small leaves if you run out of big leaves).
Place the stuffed cabbage rolls in a 9 by 13inch baking dish, folded side down. Pour the salsa over the cabbage rolls and bake, covered, for 1 hour or until the cabbage is very tender.
Transfer cabbage rolls to individual plates or a serving platter, sprinkle with the Cotija cheese and serve warm.
c.1997, M.S. Milliken & S. Feniger, all rights reserved