Boil the 4 tomatillos in a small pot for 5 to 6 minutes until they soften and turn a lighter green.
Meanwhile, roast the poblano pepper over an open flame or hot skillet, turning often until the skin is charred. Place in a plastic bag for 5 minutes so it steams, then peel, deseed and transfer to a blender.
Add tomatillos, 1/4 onion, garlic, 1/4 cup cilantro, 1/4 cup crema, 1/4 milk and salt. Blend until smooth and creamy. Set aside.
Next fry the tortillas. Heat about 1 cup of vegetable oil in a deep skillet. Fry the tortilla triangles in batches until golden and crispy. Drain on paper towels.
In a large skillet, sauté the sliced white onion in a bit of oil until translucent (2–3 minutes). Pour in the creamy green sauce and cook over medium heat for 2–3 minutes, stirring constantly. If it gets too thick, add a splash more milk.
Turn off the heat and add the fried tortillas to the skillet. Gently fold them into the sauce until well coated. Cover and let sit for 1 minute.
Place a generous portion of saucy chilaquiles on each plate. Top with the shredded chicken, evenly spread.
Garnish with queso fresco, a few spoonfuls of crema, pickled red onions and fresh chopped cilantro. Serve immediately while warm and slightly crunchy. Add sunny side up eggs or a side of refried beans for extra protein, if desired.