Chicken and Cheese Enchiladas

1 tablespoon olive oil, plus more for greasing  
Kosher salt and freshly ground pepper  
1 lb baby spinach  
1 yellow onion, diced  
1 clove garlic, minced  
2 cups shredded cooked chicken  
½ cup sour cream  
1 cup shredded mozzarella cheese  
½ cup shredded white Cheddar cheese  
½ cup shredded yellow Cheddar cheese  
2 tablespoons chopped fresh cilantro, plus more for garnish  
2 cans (15 oz each) green enchilada sauce  
6–8 flour tortillas  
2 green onions, white and pale green parts, thinly sliced  

SERVES 6–8 

1. Preheat the oven to 350°F. Lightly grease a large cast-iron skillet. 

2. Bring a large saucepan of salted water to a boil over high heat. Add the spinach and cook until wilted but still bright green, 2–3 minutes. Rinse under cold running water and drain well, then coarsely chop. Set aside. 

3. In a large nonstick skillet over medium-high heat, warm the oil. Add the onion and garlic, season with salt and pepper, and cook, stirring occasionally, until the onion is translucent, 4–6 minutes. Let cool. 

4. In a large bowl, stir together the onion mixture, spinach, chicken, sour cream, half of the mozzarella and Cheddar, and the cilantro. 

5. To assemble the enchiladas, spread 1 cup of the enchilada sauce in the prepared skillet. Pour 2 cups of the sauce into a pie dish or a shallow bowl. Using tongs, dip a tortilla into the sauce. Place the tortilla on a work surface, add a few tablespoons of the chicken filling down the center, and roll up the tortilla. Place the enchilada, seam side down, in the skillet. Repeat with the remaining tortillas and filling. Drizzle all of the remaining sauce, including any left in the pie dish, evenly over the enchiladas, and sprinkle with the remaining mozzarella and Cheddar. 

6. Transfer to the oven and bake until the cheese is melted and the sauce is bubbling, 30–35 minutes. Garnish with the green onions and cilantro and serve right away.