Cheese Enchiladas with Red Chile Sauce

Steps

1. Wipe the dried ancho and guajillo chiles with a damp towel, snip off the stems with scissors, slit them lengthwise, and pull out the seeds and pale veins: that is where the bitterness hides, and removing it leaves the sauce fruity and mellow.
2. Heat a heavy skillet over medium heat with no oil. Lay the chiles flat and press them down with a spatula for 20 to 30 seconds per side, until they blister, darken by one shade, and smell of cocoa and prunes. Pull them off at the first wisp of smoke: a blackened chile turns the sauce acrid.
3. Bring the vegetable broth to a simmer, pour it over the chiles in a bowl, hold them under with a plate, and let them rehydrate for 15 minutes, until they are as supple as wet leather.
4. Meanwhile, roughly slice 1 white onion and finely chop the second. In a saucepan, heat 1 tablespoon of the neutral oil over medium heat and cook the sliced onion for 5 minutes, until soft and blond, then add the crushed garlic for 1 minute. Tip everything into a blender with the chiles and their broth, and blend for 1 to 2 minutes, until the sauce is smooth and glossy.
5. Return the saucepan to medium heat with 2 tablespoons of the neutral oil, add the flour, and whisk for 2 minutes, until the roux smells nutty and turns sandy beige. Add the cumin, oregano, and tomato paste, stir for 30 seconds, then pour the blended sauce through a fine sieve into the pan, whisking. Simmer at a gentle bubble for 10 minutes, until it coats the back of a spoon. Season with the salt, sugar, and cider vinegar, then taste: it should be deep, barely sweet, with a hint of tang.
6. Preheat the oven to 400°F (200°C). Toss the shredded cheddar and Monterey Jack together. Set aside 100 g (about 1 cup) for the top. Stir the chopped onion into the rest, keeping 2 tablespoons of onion for garnish.
7. Heat the remaining neutral oil in a skillet over medium-high heat to about 350°F (180°C): the edge of a tortilla should sizzle on contact. Dip each corn tortilla in the oil for 5 to 10 seconds per side, just until pliable and covered in small bubbles but not crisp, then drain on paper towels. This quick bath makes them bendable and keeps them from falling apart in the sauce.
8. Spread a ladle of sauce over the bottom of a 9 x 13 inch (23 x 33 cm) baking dish. Dip each tortilla in the sauce, place about 20 g (3 tablespoons) of the cheese and onion filling along one edge, roll it up snugly, and set it in the dish seam side down. Pack all 12 enchiladas tightly side by side.
9. Pour the rest of the sauce over the top, making sure the ends are covered, or they will dry out and harden in the oven. Scatter the reserved 100 g of cheese over the sauce and bake for 15 to 20 minutes, until the cheese is bubbling and browned in spots and the sauce is simmering at the edges.
10. Let rest for 5 minutes so the sauce can settle. Sprinkle with chopped cilantro and the reserved onion, and serve with sour cream, 3 enchiladas per person.