Preheat broiler. Roast chiles under broiler on cookie sheet lined with parchment or Al foil until skin is brown and charred, 6-7 min per side, turning as required for all sides. Place in bag and allow to cool to touch. Make slit down one side and remove stem and seeds. Lay flat and scrape off blackened skin. Alternatively use propane torch to scorch skin, cut in half and remove innards, lay flat and scrape off char. If using torch heat finished chiles in microwave or oven to slightly soften.
Preheat oven temperature to 350 deg.
Line the bottom of a 9×13 baking pan with the chiles. Layer the cheese evenly on top of the chiles. Spread cooked chicken evenly over the cheese.
In medium bowl mix flour with a small amount of evaporated milk until it forms a paste, then whisk in remaining milk and sour cream. Beat in eggs one at a time. Pour evenly over the chicken.
Bake in preheated oven for 40 min. or until the center of the pie is firm.
Spread salsa over the top, and bake for 15 min.
Allow to cool 10 min. before serving.
9×13=117in^2, 8×8+9×9=145in^2 (x1.23)