Place the jalapeños, onion and garlic cloves into a pot and pour in enough water to cover them. Over medium heat, bring to a simmer and cook until the vegetables are all soft and a fork can easily be inserted into the jalapeños. Drain and place into a blender. Add the orange juice, sea salt, pilloncillo or brown sugar and the dried oregano; blend until it is a smooth and thick sauce. Taste the sauce and adjust the sugar and/or salt if necessary.
Heat the oil in a large pan, once hot fry the chicken breasts on both sides for about 5 minutes (on each side). Gently pour in the sauce (from the blender), chicken broth and turn the heat to medium-low, cover the pan and simmer until the chicken is cooked through, very soft and pulls apart easily. (Do not let the liquid evaporate, if this happens you can add more chicken broth.) Again taste and adjust the seasonings if desired. About 5-8 minutes before serving: mix the masa harina with the water then pour into the chicken to thicken the sauce, allow to simmer for a few minutes. Serve with warm corn tortillas and refried beans or white or Mexican rice if desired. And if you'd like sprinkle some pepitas/sunflower seeds over the dish.
Notes
*Jalapeño tip: To make the sauce milder you can cut the peppers in half and completely remove the seeds and vein from inside each chile. Additionally you can use less peppers if desired — but please be aware that I’ve only tested the recipe with exactly 200 gm of jalapeños.
**Bitter orange tip:To substitute the naranja agria use a mixture of half grapefruit-half lime juice. Additionally you could use a mixture of half orange juice-half lime juice -- but please use fresh squeezed juices! The taste will not be the same but it will help in tenderising the meat and also add the tart citrus taste.
Recipe by Spicie Foodie ™ at https://www.spiciefoodie.com/2014/03/29/chicken-breasts-in-jalapeno-and-sour-orange-sauce/