Roast the peppers by placing them on an open gas flame, turning them frequently with tongs until all sides are charred black, 7 to 10 minutes. (Alternatively, the peppers can be roasted under a broiler or on top of a gas or charcoal grill.) Place the blackened peppers in a plastic or paper bag and let rest until cool enough to handle, about 15 minutes. Peel the peppers, split in half lengthwise, and discard the seeds and stems. Roughly chop and set aside.
Bring a large pot of salted water to a boil. In 3 batches, add the spinach and blanch for 15 seconds. Remove with a slotted spoon and cool in an ice bath. Remove from the ice bath and squeeze out the excess water. Chop and set aside.
In a large saucepan, melt 4 tablespoons butter over medium-high heat. Add the onions and cook, stirring, until very soft, 3 to 4 minutes. Add the garlic, chili powder, salt, black pepper, and cayenne and cook, stirring, for 45 seconds. Add 1/4 cup flour and cook, stirring with a wooden spoon, to make a light roux, 2 minutes. Gradually add the half-and-half and cook, stirring, until thick, 2 to 3 minutes. Add the spinach and stir to incorporate. Remove from the heat and fold in half of the chopped poblanos. Adjust the seasoning to taste. Fold in the cubed Pepper Jack and queso fresco cheeses and set aside.
In a small bowl, combine the grated Pepper Jack and Parmesan cheeses. Set aside.
Preheat the oven to 350?F.
In a medium skillet, heat 2 tablespoons vegetable oil over medium heat. Add the tortillas, 1 at a time, to the hot oil and cook, turning, until soft and pliable, 15 seconds per side, adding more oil as needed. Remove from the pan and place on a work surface.
Place about 1/2 cup of the spinach mixture into the center of each tortilla and roll up into a cylinder. Place the cylinders, seam side down, in a single layer across the bottom of a 9 x 13-inch casserole.
In a medium saucepan, melt the remaining 4 tablespoons butter over medium heat. Add the remaining 1/4 cup flour and cook, stirring constantly with a wooden spoon, to make a light roux. Slowly add the Chicken Stock and cook, stirring, until thickened, 3 to 4 minutes. Add the cream and cook, stirring, until thick, about 2 minutes. Add the remaining poblanos and cook for 1 minute.
Pour the sauce over the filled enchiladas and bake for 20 minutes. Remove from the oven and cover evenly with the remaining grated cheeses. Return to the oven and bake until the cheeses are melted and bubbly and the enchiladas are completely warmed through, 10 to 15 minutes. Remove from the oven and let sit for 5 minutes before serving.
Makes 6 servings