How to Make It
Preheat the oven to 400°. In a large ovenproof skillet, combine the tomatoes, garlic, serranos, onion, poblano and olive oil and season with salt and pepper. Cook over moderately high heat until the vegetables are sizzling and the skins of the chiles begin to blister. Transfer the skillet to the oven and roast the vegetables for 20 minutes, until tender and lightly browned. Leave the oven on.
Return the skillet to the stove. Stir in the tomato paste and chipotle and cook over moderate heat until the tomato paste caramelizes a bit, about 2 minutes. Add the chicken stock and bring to a boil, scraping up any browned bits on the bottom of the skillet. Remove from the heat and let cool for 15 minutes.
Working in batches if necessary, puree the contents of the skillet in a blender until completely smooth. Wipe out the skillet. Strain the sauce into the skillet. Stir in the sugar and lemon juice and season with salt and pepper. Keep warm over moderate heat.
In a large skillet, heat the olive oil until shimmering. Add the mushrooms, season with salt and cook over moderately high heat until softened and beginning to brown, about 7 minutes. Stir in 1 cup of the enchilada sauce and the chicken.
Wrap the tortillas in a damp paper towel and warm them in a microwave oven until soft and pliable, about 1 minute. In a bowl, toss the cheddar with the Monterey Jack.
Brush a 9-by-13-inch glass baking dish with some of the vegetable oil. Arrange the tortillas on a work surface. Spoon 1/4 cup of the chicken filling in the center of each tortilla and top with 1/4 cup of the cheese. Roll up the enchiladas and arrange them in the prepared baking dish. Brush with the remaining vegetable oil and pour the remaining sauce on top, brushing to distribute it evenly. Sprinkle the remaining 1 cup of cheese over the sauce. Bake the enchiladas for 30 minutes, until the sauce and cheese are bubbling and the edges of the tortillas are browned and crisp. Serve hot, with Sour Cream Slaw, sour cream and hot sauce.