Preheat oven to 350°F.
In a medium sauce pan, make a roux. Melt butter over medium heat. Add onions and Store leftovers in an airtight container in the fridge. Sour cream chicken enchiladas will last 3-4 days, and they can be reheated in a 350ºF oven or in the microwave until they’re warmed through.
Reduce heat to low and add in sour cream and green chilies. Remove from heat and set aside.
In a large mixing bowl, combine black beans, chicken, 1 cup of pepper jack cheese and 1 cup of the sour cream sauce you set aside.
Apply cooking spray or grease a 9in X 13in baking pan. Coat the bottom of baking pan with ½ cup of sour cream sauce.
Fill each tortilla with ½ cup of enchilada filling. Roll and place seam side down on baking pan.
Pour remaining sour cream sauce over the enchiladas and top with remaining cheese.
Bake in oven on middle rack, uncovered for 20-25 minutes. The cheese should be melted and the tortillas should start to brown on edges.
Move baking dish to top rack and broil on high for about 3 minutes. The cheese should start to brown but not burn, so watch carefully.
Top with your favorite garnish like fresh cilantro, red onions or jalapeños.