Peel the tomatillos and cut the jalapeño in half lengthwise, then use a spoon to scrape out the seeds and membrane from the bottom to the top of each half.
In a pot, add the tomatillos and jalapeno pepper. Pour in some water and simmer over high heat for about 10 minutes until they are soft.
Meanwhile, roast the poblano peppers until the skins are charred. Place them in a closed container to sweat. Once cooled, peel off the skins and remove the seeds and stems. If you prefer, you can also roast the tomatillos and jalapeno peppers.
In a blender, add the tomatillos, roasted poblano peppers, serranos, onion, garlic, and cilantro. Pour in the chicken broth and blend until smooth.
In a saucepan over medium-high heat, warm the oil until it is smoking. Quickly add the tomatillo sauce, stirring constantly, until the sauce begins to bubble. Add the chicken bouillon and stir well. Adjust seasoning as needed. Reduce the heat to low and cook until the sauce starts to thicken, about 5 minutes more.