1 lb. (6 to 8) tomatillos, husked and rinsed
1 medium white onion, sliced about ¼ in. thick
3 garlic cloves, peeled
Hot green chiles to taste (2 to 3 serranos, or 1 to 2 jalapeños), stemmed
1 1/2 tbs. vegetable oil, plus extra for vegetables and maybe tortillas
2 cups vegetable or chicken broth, plus a little extra if needed
1/2 cup Mexican crema, crème fraîche, or heavy whipping cream
8 cups cubed vegetables (about 1/2-in. each) such as carrots, onions, turnips, mushrooms, and broccoli
12 corn tortillas
1 cup shredded Mexican cheese like asadero, or Monterey Jack or cheddar
Roast tomatillos, sliced onion, garlic, and chiles on rimmed baking sheet 4 in. below preheated broiler until tomatillos are soft and blackened in spots on one side, 4 to 5 minutes. Turn vegetables over; broil about 4 minutes longer. Remove and reduce oven temperature to 400°F.
Scrape tomatillo mixture into food processor or blender. Process until smooth purée. Heat 1 1/2 Tbsp. oil in medium-large pot over medium-high heat. When drop of purée sizzles in oil, add remainder of purée. Stir constantly for several minutes until darker and thicker. Add broth and crema, reduce heat to medium-low, partially cover, and simmer for about 30 minutes.
Spread cubed vegetables on rimmed baking sheet. Drizzle with oil, sprinkle with salt, and mix to coat evenly. Place in oven and roast, turning vegetables regularly, until crunchy-tender, about 25 minutes (reduce roasting time for broccoli and other green vegetables by 5 to 10 minutes).
If sauce has thickened and is no longer consistency of light cream soup, stir in a little more broth (or water). Taste and season with salt, about 1 tsp. Lightly brush both sides of each tortilla with oil. Stack, wrap in damp paper towels, and microwave on high (100%) for 1 minute to warm and soften. Or you can do what I did: cover two tortillas at a time with a damp paper towel. Microwave for 45 seconds. Roll some of the filling inside and place them side by side in the baking dish. Repeat with two more tortillas until your filling is gone.
Spread about 1 cup sauce over bottom of 13-by-9-in. baking dish. Working quickly, roll equal portion of roasted vegetables into each tortilla while tortillas are still hot and pliable. Place them side by side in baking dish. Douse evenly with remaining sauce. Sprinkle with cheese. Bake until enchiladas are heated through and cheese begins to brown, about 10 minutes. Garnish with onion rings and cilantro sprigs.