For sauce:

Cook spinach according to package instructions. Drain well. Set aside. Melt butter in heavy medium skillet over medium heat. Add flour and stir mixture 2 minutes; do not brown. Gradually whisk in whipping cream and milk. Simmer until thickened, about 5 minutes. Stir in spinach, cilantro, green onion, chilies, cumin, coriander and red pepper. Puree in batches in processor until almost smooth. Season with salt and pepper. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to room temperature before using.)

For enchiladas:

Heat oil in heavy small skillet over medium-high heat. Using tongs, briefly dip each tortilla in oil to soften, about 15 seconds per side. Transfer to paper towels and drain. Combine cheeses in large bowl; set aside 1 1/2 cups for topping. Combine onion and cilantro in small bowl. Place 1/4 cup cheese mixture in center of 1 tortilla. Spoon 2 teaspoons onion mixture over. Roll up tortilla. Place seam side down in large glass baking dish. Repeat with remaining tortillas, cheese and onion, using 1/4 cup cheese for each. (Can be made 1 day ahead. Cover and chill.)

Preheat oven to 375F. Stir sour cream into sauce; pour over enchiladas. Sprinkle with reserved 1 1/2 cups cheese. Bake until cheese melts and enchiladas are heated through, about 25 minutes.