1) Preheat oven to 350° F. Season the meat with salt and pepper. Put the oil in a Dutch oven over medium-high heat. Dredge half the beef in flour, shaking off any excess. Brown well in the hot oil, then remove to a platter with a slotted spoon. Repeat with the remaining beef, then the pork.
2) Pour off any fat from the pot. Add the onions and garlic and sauté until soft. Add the broth and bring to a boil, scraping the bottom of the pan with a wooden spoon. Add the meat back to the pot and simmer gently, covered, for 45 minutes.
3) Meanwhile, toast the dried chilies in the oven for 5 minutes until puffed and fragrant. Using rubber gloves, remove the stems and seeds. Break up the chilies into coarse pieces. Put them in a bowl, pour boiling water over them and let them soak for 15 minutes. Purée them in a blender with about 1/4 cup of the soaking water, enough to form a smooth paste.
4) Toast the cumin seeds in a heavy skillet over medium-low heat, stirring periodically, until fragrant. Then grind. Add the chile paste, cumin, oregano, tomato sauce and sugar to the meat mixture and simmer gently for an additional 1 1/4 hours, partially covered. Stir periodically. Add the jalapeno, if desired. Add salt as needed. Cook for another 1/2 hour, partially covered. Serves 8.