Start by heating the neutral oil in a skillet over medium heat, then add the 1/4 white onion, garlic cloves, tomatoes, serranos, and chiles de árbol.
Fry for about 8 minutes, or until the tomatoes soften and the onion becomes translucent.
Pour in 3/4 of the beer and let the mixture simmer over medium-low heat for 10–12 minutes to allow the flavors to meld.
Transfer the cooked onion, garlic, and chiles de árbol to a blender and blend until smooth.
Add the softened tomatoes and serrano peppers to the blender and pulse until you reach your desired salsa consistency.
Pour the blended salsa into a serving bowl.
Stir in the remaining beer, chopped white onion, chopped cilantro, and salt to taste.
Mix to combine and serve.