Mix shredded chicken, cheeses, sour cream, onion, and seasonings in a bowl until well combined to create a creamy filling that spreads evenly in tortillas.
Prepare a roux by melting butter and whisking in flour, then gradually add chicken broth and cook until thickened before stirring in sour cream and spices off heat.
Fill each tortilla with the chicken mixture, roll tightly, and arrange seam-side down in a greased baking dish to maintain structure.
Pour the white sauce evenly over enchiladas and top with shredded cheese to ensure full coverage and even baking.
Bake at 180°C (350°F) for 25–30 minutes until bubbly and golden, then allow to rest briefly before serving for best texture.