Toast the ancho, pasilla, and New Mexican dried peppers in a skillet over medium heat for 1-2 minutes until fragrant and slightly darkened. Remove, cool, and discard stems and seeds. Soak the peppers in hot water for 20 minutes until soft. Blend with a bit of soaking water until smooth.

Season beef chuck with cumin, salt, and pepper. Heat olive oil in a large pot over medium-high heat, add beef, and sear for 6-7 minutes until browned on all sides. Remove and set aside.

In the same pot, add onion, jalapeños, and optional serrano peppers. Sauté for about 5 minutes until onions are translucent. Add garlic and cook for an additional minute.

Return seared beef to the pot, stir in chili paste, pour in beef stock and water. Add brown sugar, Worcestershire sauce, and masa harina. Bring to a boil.

Once boiling, reduce heat to low, cover, and simmer for 2 hours, stirring every 30 minutes. Adjust consistency with more water if needed.