Sour Cream White Chicken Enchiladas

Preheat the oven to 350°F and cook fresh tortillas (if needed), according to the package directions.
Melt the butter in a medium-sized skillet or saucepan over medium-high heat on the stovetop. When butter is melted, add the diced onions and saute for 3-4 minutes until tender and slightly translucent.
Sprinkle the flour over the sauteed onions and whisk to combine. Continue to cook, while whisking for another 2 minutes.
Add the green chilies and chicken stock and whisk to combine. Bring the sauce to a boil and continue to cook, while whisking for another 3 minutes until the sauce thickens.
Remove the sauce from the heat and whisk in sour cream, salt, and pepper.
Ladle approximately ½ cup of the sauce into a 9x13 baking dish, to barely cover the bottom.
Mix the shredded chicken and half of each of the shredded cheeses in a medium bowl.
Lay out the tortillas on a table or countertop and evenly divide the chicken and cheese mixture into the center of each tortilla.
Roll each tortilla tightly and place them seam-side down into the baking dish.
Pour the remaining sauce over the tortillas to cover them, and sprinkle the remaining cheese on top.
Cover the pan with foil and bake the enchiladas for 20-30 minutes or until the cheese is melted and the filling is bubbly. For crispy edges and browned cheese, broil the enchiladas uncovered for a few minutes.