Make the salsa: In a medium saucepan, place tomatillos, tomatoes, chiles, garlic and onions. Bring to a boil, then simmer until tomatoes are soft, about 10 minutes.
Remove from saucepan and place vegetables in blender jar. Process until smooth. Season to taste with salt and reserve sauce.
Make the pie: In a medium frying pan, heat vegetable oil. Soft-fry tortillas for 20 seconds per side. Drain on paper towels and repeat until all tortillas are done.
In a square pyrex dish, place a layer of 5 tortillas on the bottom. Top with 1 cup shredded chicken, then top with 2/3 cup salsa, 1 cup shredded cheese and 1/2 cup crema. Repeat with additional tortillas, chicken, salsa, cheese and crema for another 3 layers. For the top layer, you place the tortillas, and top with only salsa, cheese, and crema.
Place pyrex in a pre-heated 350°F oven and bake for about 30 minutes, until cheese is bubbly.
Remove from oven and let pastel rest for about 10 minutes. Cut into squares and serve.