Preheat oven to 350°F. Grease a 9×13-inch baking pan and set aside.: Take note of the even, warm glow inside the oven as it approaches temperature, which ensures the enchiladas bake evenly and the cheese melts predictably. A well greased pan prevents sticking and helps the bottom edges become pleasantly crisp without tearing when serving. A common mistake is skipping the greasing, which can cause portions to stick; also avoid setting the pan in the oven before it reaches temperature, which can alter bake timing.
In a small saucepan, melt the butter over medium heat. Add in the onion, garlic, salt, and cumin, cook for a minute until softened.: As the butter melts, you should smell a warm, slightly sweet aroma, and the onion will become glossy and translucent, signaling it has softened. The brief cook time releases aromatic oils from the garlic and the cumin will bloom, deepening its flavor. Avoid high heat which can brown or burn the aromatics, creating bitter notes that will carry through the sauce.
Stir in the flour and let it cook for about 30 seconds until it forms a paste.: The moment the all purpose flour hits the fat, you will see a pasty, cohesive mixture form; this is the roux that thickens the sauce. Cook briefly to eliminate the raw flour taste but do not let it darken, as color change indicates the roux is cooking too long and will alter the sauce color and flavor. A frequent error is undercooking the roux, which leaves a floury graininess in the finished sauce.
Gently and gradually whisk in the chicken broth, continue to whisk until the mixture reaches a smooth, sauce-like consistency. If you add too much liquid, let the mixture simmer for a minute to reduce.: As you whisk in the chicken broth , watch the sauce become glossy and viscous, free of lumps. The gentle simmer will create soft bubbling sounds and a scent of savory broth that melds with the spices. If it becomes too thin, a brief simmer will concentrate it back to the right body. Avoid dumping the broth all at once, which can cause lumps and uneven texture.
Stir in the sour cream and green chiles, remove from heat, and set aside.: When you fold in the sour cream , the sauce should turn silkier and slightly paler, and the little flecks of green chiles will add visual interest and a gentle vegetal note. Removing it from heat prevents curdling and keeps the texture smooth. A common slip is continuing to cook after adding dairy, which can break the sauce and create a grainy texture.
In a medium bowl, combine the shredded chicken, black beans, green onions, lime juice, 1 cup of cheese, and 1 cup of enchilada sauce.: As you toss the filling, the chicken fibers absorb the sauce and aromatics, while the black beans lend a creamy bite. The scent of lime juice will introduce a bright top note that balances richness. Mixing evenly ensures each tortilla gets a consistent flavor; avoid over stirring which can mash the beans and turn the filling pasty.
Pour 1/2 cup of the enchilada sauce on the bottom of the prepared baking pan.: The quick sizzle as the sauce hits the warm pan signals the start of flavor layering; this base prevents the tortillas from sticking and ensures the bottom edges soak up flavorful moisture rather than turning dry. Spread it evenly so all enchiladas sit in the sauce. A common oversight is skipping this step, which increases the likelihood of dry patches and sticking.
Fill each tortilla with about 1/2 cup of enchilada filling.: As you spoon filling into each warmed flour tortilla , feel for a balance between generous filling and ability to roll. The filling should be moist but not runny, so the edges roll cleanly. If you overfill, the tortilla will tear or the pan will become soggy; aim for consistent portions for even baking.
Place the enchiladas, seam side down, into the baking pan and pour the remaining sauce over the enchiladas. Sprinkle the remaining cheese on top.: When arranged seam side down, the enchiladas hold their shape and present a neat top for saucing and cheese. Pouring the rest of the sauce provides an even coating that keeps them moist, and the shredded Monterey Jack cheese will melt into a golden, bubbling layer. Avoid pouring too much sauce unevenly, which can cause parts to be overly soggy and other parts dry.
Bake uncovered in the preheated oven for 20-30 minutes, or until the cheese has melted and the edges of the tortillas are starting to become brown and crispy.: During baking you will hear gentle bubbling and smell a toasty, melded aroma of cheese and spices. Visually, the cheese should be melted and starting to brown in spots, and the tortilla edges will crisp slightly. Overbaking can dry the filling, so remove when bubbling and browned to your preference; check at the 20 minute mark to avoid brittleness.
If desired, top with fresh cilantro, chopped onion, chopped jalapeño peppers, avocado slices, and cotija cheese.: The final garnishes add color, texture, and temperature contrast, with the cool avocado and bright cilantro offsetting the warm, cheesy interior. Sprinkle toppings just before serving to keep them fresh and vibrant. A frequent mistake is adding delicate garnishes too early, which causes them to wilt and lose their appeal.