Step 1: Begin by preparing your homemade enchilada sauce. In a medium saucepan, melt butter or heat oil over medium heat. Whisk in flour and cook for 1-2 minutes until a light roux forms. Gradually whisk in chili powder, cumin, oregano, garlic powder, and a pinch of cayenne pepper (if using). Cook for another minute until fragrant.
Step 2: Slowly pour in the chicken broth, whisking constantly to prevent lumps. Bring the sauce to a simmer, then reduce heat to low and let it thicken, stirring occasionally, for about 10-15 minutes. Season with salt and pepper to taste. Keep warm.
Step 3: While the sauce simmers, prepare your chicken filling. In a large bowl, combine the shredded cooked chicken with half of the chopped onion, half of the green chilies, and 1/4 cup of the prepared enchilada sauce. Mix well to ensure the chicken is evenly coated and seasoned.
Step 4: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish. Pour a thin layer of enchilada sauce (about 1/2 cup) on the bottom of the prepared dish.
Step 5: Briefly warm your corn tortillas. You can do this by quickly dipping each tortilla into the warm enchilada sauce (just for a few seconds to soften) or by microwaving a stack wrapped in a damp paper towel for 30-60 seconds. This prevents them from cracking.
Step 6: Take one softened tortilla, spoon about 1/4 cup of the chicken mixture down the center, and sprinkle with a generous pinch of shredded cheese. Roll the tortilla tightly and place it seam-down in the baking dish. Repeat with the remaining tortillas and filling until the dish is full.
Step 7: Pour the remaining enchilada sauce evenly over the rolled tortillas, ensuring every enchilada is well covered. Sprinkle the remaining shredded cheese over the top of the sauce.
Step 8: Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly and the sauce is simmering. For a slightly golden-brown top, you can broil for the last 1-2 minutes, watching carefully to prevent burning.
Step 9: Remove the enchiladas from the oven and let them rest for 5-10 minutes before serving. This allows the sauce to settle and makes for easier serving.
Step 10: Garnish with fresh cilantro, the remaining chopped onion, and a dollop of sour cream or crema, if desired. Serve hot and enjoy!