How to Make It
In a blender, combine the tomatoes with their reserved 1/2 cup of liquid and the chipotles; blend until almost smooth.
In a very large, deep skillet, heat the oil. Add two-thirds of the onion and cook over moderately high heat until browned around the edges, about 6 minutes. Add the garlic and cook for 1 minute. Pour in the tomato puree and simmer, stirring, until slightly thickened, about 5 minutes. Stir in the stock and boil the sauce over moderately high heat until slightly thickened, about 2 minutes. Season with salt and remove from the heat.
Gently stir the tortilla chips into the sauce, making sure they are well coated. Top with the remaining onion, the shredded chicken and the Parmesan cheese. Dollop the sour cream over the chilaquiles, sprinkle with the cilantro and serve immediately.
Queso añejo is an aged Spanish white cheese that's slightly salty.