Add flour and whisk constantly until thickened and just starting to turn light brown, 2 to 3 minutes.
Slowly add milk, whisking constantly.
(Do not boil.)
Remove from heat and, a handful at a time, whisk in Cheddar and Parmesan until smooth.
Stir in 1/2 teaspoon salt.
(Reserve 2 1/2 cups for another use.)
Preheat oven to 400 degrees F. Coat a 9-inch (or similar size) baking dish with cooking spray.
To prepare enchiladas: Heat avocado (or canola) oil in a large skillet over medium-high heat.
Stir green chiles into 1 1/2 cups of the warm cheese sauce.
Arrange one-third of the tortilla wedges in the prepared baking dish, overlapping as necessary to fit.
Top with half the beef mixture and 1/2 cup of the cheese sauce.
Repeat with half the remaining tortillas, the remaining beef mixture and 1/2 cup of the cheese sauce.
Top with the remaining tortillas, the remaining 1/2 cup cheese sauce and tomato.
Bake until bubbling, about 15 minutes.
With the motor running, slowly add oil and puree until creamy.
Top the casserole with the remaining 1/4 cup cilantro and cut into 4 servings.
Serve with the slaw.
To make ahead
Prepare cheese sauce (Step 1).
Transfer to a 4-cup heatproof container and let cool to room temperature, about 30 minutes.
Refrigerate for up to 5 days.
Prepare dressing (Step 5); refrigerate for up to 1 week.
- Daily Values (DVs) are the recommended amounts of nutrients to consume each day.
(-) Information is not currently available for this nutrient.
