Preheat oven to 450 degrees F. On a rimmed baking sheet, roast the tomatillos, poblanos, onion, garlic and serrano pepper for 15-20 minutes, until the tomatillos are bubbling and juicy.
Remove the stems and seeds from the peppers. Then transfer the roasted vegetables and juices to a food processor. Add the cumin, salt, spinach, and cilantro. Pulse the mixture until well combined but still chunky.
In a large bowl combine and shredded chicken with half of the fresh salsa verde, and half of the shredded cheese. Mix well, then salt and pepper to taste.
Change the temperature of the oven to 350 degrees F. Set out a 9X13 inch baking dish.
Pour the remaining salsa verde in a shallow pan for assembling. Dip the tortillas in the salsa, coating on both sides, to soften.
Put a scoop of the shredded chicken mixture on top of each tortilla. Fold the tortillas over the filling and roll to close. Place the tortillas in the baking dish, ends down. You may have to squeeze them into two rows.
In a mixing bowl, combine the sour cream, half & half, and the last of the salsa verde. Mix until smooth. Pour the creamy topping over the enchiladas and top with the remaining shredded cheese.
Bake for 30 minutes until bubbly. If the cheese starts to brown, loosely cover the top with foil. Garnish with cilantro and serve warm.
This recipe is gluten free if you use corn tortillas.