Heat a small, heavy skillet over medium-high heat. Add the cumin and coriander and toast, giving the pan an occasional shake, until the seeds are fragrant, about 5 minutes. Grind the seeds in a spice grinder or crush them in a mortar and pestle. In the same hot pan, toast the fresh oregano, if using (don't toast dried oregano). Remove the leaves after they've begun to dry out but before they lose all of their green color, about 3 minutes. Set aside.
In a large, heavy-based skillet, Dutch oven, or stockpot, heat the oil until very hot. Brown the meat in the oil in batches (add more oil to the pan as needed), being careful not to crowd the pan or the meat will stew in its own juices and not brown. Transfer the browned meat from the pan to a plate lined with paper towels. Don't clean the skillet after browning the meat.
To the same skillet, add the onion, garlic, jalapeños, masa harina, pasilla powder, the toasted ground cumin and coriander, and toasted (or dried) oregano. Stir over medium-high heat until the onion begins to soften, 5 to 8 minutes. Return the meat to the skillet; add the tomatoes, whole dried chiles, beer, chocolate, and water or stock. Simmer until the meat is fork-tender, about 1-1/2 hours. Remove the whole chiles before serving.