Heat the olive oil in 12-inch non-stick skillet over medium high heat. Add the garlic, tomatillos, and onion. Sauté until the vegetables are slightly charred. Set aside. On the stove, hold each Poblano pepper with tongs and place them directly over a high flame. Allow the skin to blacken on all sides. Put the charred Poblanos in a sealed plastic bag for 3 minutes. Place each Poblano under running water and peel off the skin. Cut in half and remove the stem, seeds, and veins. In a blender, place the sautéed vegetables, Poblanos, chicken broth, and salt. Blend on high for about 3 minutes or until smooth. Pour the mixture into a 4-quart saucepan over medium-high heat and cook for 15 minutes. Heat ¼ cup oil in a 2 quart non-stick saucepan over medium high heat. In batches fry the tortilla strips, turning constantly with tongs, for 2 to 5 minutes or until crispy and light brown. Place on a plate lined with paper towels to drain the oil. Meanwhile, in small bowl, mix the sour cream and whole milk until smooth. Pour the soup into serving bowls. Top with the tortilla strips, shredded chicken, avocado, cilantro, and Cotija cheese. Drizzle with the sour cream sauce.