Preheat the oven to 425 ℉. Spray two 9×9 inch glass dishes (or one large 9×13 inch glass dish) with nonstick spray.: The kitchen fills with a steady wave of warm air as the oven climbs to temperature, and you may hear the hum and occasional click as it stabilizes. Getting the oven hot ensures the top of the enchiladas becomes slightly golden and the sauce bubbles up around the edges, which is a key visual cue that they are done. One reason this matters is that a properly preheated oven produces even baking, preventing soggy tortillas. A common mistake is putting the dish into an oven that is not fully heated, which can lengthen bake time and leave the interior less cohesive.
In a medium saucepan, melt the butter over medium heat. Whisk in the flour and cook, stirring 1 minute. Gradually add the broth and cook, whisking, until thick (about 5 minutes). Remove from heat. Whisk in the sour cream and taco sauce and set aside.: The surfaces should glisten lightly to prevent sticking, and the nonstick coating also helps the underside of the enchiladas brown a touch. Using glass gives you visual feedback, so you can see bubbling around the edges. If you skip this step, cheese can glue the tortillas to the dish, making serving messy and difficult. Wipe any excess spray off the rim so it does not burn in the oven.
Lay out a tortilla onto a working surface. Place 2 tablespoons of Jack cheese, 1/4 cup chicken, onions and asparagus down the center of the tortilla. Spoon 3 tablespoons of the sauce on top of the mixture. Roll and place seam down. Place 6 enchiladas in each dish. Sprinkle with Jack cheese, sauce and Parmesan.: As the butter melts it will foam and then settle, releasing a warm, nutty aroma. This is the foundation for the roux, and medium heat keeps the butter from browning too quickly. If the butter browns, the flavor may become more toasty than desired for this creamy sauce. Stir gently to promote even melting and avoid pockets of overheated fat.
Bake for 25 minutes, or until light golden color and bubbly.: The mixture will thicken and take on a pasty texture, and you may notice a faint toasted scent as the raw flour cooks off. This brief cook prevents a floury taste in the finished sauce and ensures smooth thickening when liquid is added. Stir constantly to avoid clumps forming, and use a whisk to keep the texture silky. A common mistake is undercooking the flour, which can leave a raw flavor.
Gradually add the broth and cook, whisking, until thick about 5 minutes: Pour the chicken broth slowly in a thin stream while whisking vigorously so the sauce becomes glossy and lump free. The sauce will transition from thin to creamy, and you should hear a gentle simmer as it thickens. This step builds the body of the sauce so it will cling to the filling. If you add the broth too quickly, you risk lumps, so patience and persistent whisking are key. If it flowers or separates, reduce the heat and whisk until smooth.
Remove from heat: Once the sauce reaches a velvety thickness, lift the pan off the burner to prevent overcooking. This pause avoids breaking the emulsion when you add dairy. Leaving it on the heat can cause curdling when the sour cream is incorporated. If the pan sits too long and skin forms, whisk gently to reincorporate.
Whisk in the sour cream and taco sauce and set aside: Adding the sour cream brings a tangy silkiness while the green taco sauce adds brightness and subtle spice; whisking until homogeneous gives the sauce its signature flavor and sheen. The sauce should be smooth and slightly runny, perfect for drizzling. If it seems too thin, it will still thicken in the oven as it bakes with the fillings; if clumpy, warm it gently while whisking. Avoid boiling after adding the sour cream to prevent separation.
Lay out a tortilla onto a working surface: The tortillas should be room temperature and pliable; if they are stiff, briefly warming them will make rolling easier and prevent tearing. A soft tortilla folds neatly around the filling and forms a tidy roll that bakes evenly. Cold tortillas are more likely to crack when rolled, so warm them for a few seconds in a microwave or on a skillet.
Place 2 tablespoons of Jack cheese, 1/4 cup chicken, onions and asparagus down the center of the tortilla: The filling balance here is crucial, offering a creamy, cheesy center, the savory chicken , the onion's sweet notes, and the crisp asparagus . Arrange ingredients so they form an even line; uneven distribution can cause some enchiladas to be overloaded while others are sparse. Overfilling will make rolling difficult and may cause sauce to leak during baking.
Spoon 3 tablespoons of the sauce on top of the mixture: The sauce moistens the filling and helps the cheese melt into the chicken and vegetables, creating cohesive bites. Three tablespoons provides enough moisture without making the tortilla soggy. If you add too much sauce raw, tortillas may become limp; if too little, the filling can be dry after baking. Aim for an even coating that will meld during the oven time.
Roll and place seam down: Rolling tightly but gently ensures each enchilada holds together and that the seam sits against the dish so it does not unroll while baking. A seam-down placement makes for a neat presentation and helps the tops brown evenly. If you roll too loosely the filling may spill, and if you roll too tightly you can squeeze out the sauce and compress the texture.
Place 6 enchiladas in each dish: Arrange them snugly so they support each other, which helps maintain shape while the cheese melts and the sauce bubbles. This close placement also encourages even browning across the top. If you leave too much space between rolls, the edges can crisp excessively while the centers stay softer.
Sprinkle with Jack cheese sauce and Parmesan: A final shower of Monterey Jack cheese and grated Parmesan cheese creates a luscious, golden surface that browns and bubbles invitingly. The cheeses develop flavor and texture as they melt, producing those irresistible pull-apart strands. Be sure the cheese is evenly distributed for consistent browning; clumps can burn and leave uneven texture.
Bake for 25 minutes until light golden color and bubbly: As the dish bakes you will hear gentle bubbling and see the sauce rise slightly around the edges; the top should take on a pale golden tone and the cheese should be fully melted. This baking step sets the tortillas, melds flavors, and finishes the textural transformation. Overbaking will dry the enchiladas and toughen the tortillas, while underbaking leaves the interior cooler and less cohesive, so watch for those visual cues to determine doneness.