Spray a 9Γ9 inch baking dish with non-stick spray. Slice whole canned green chiles wide open; rinse out any seeds, then drain. Arrange half of the chiles in the bottom of the dish.
Sprinkle chiles with HALF of the grated jack and cheddar cheeses. Add remaining green chiles in another layer on top of the cheese. Top with remaining jack and cheddar cheeses.
In a small bowl, whisk together eggs, flour, milk and salt until fully blended. Pour this mixture over the casserole, distributing evenly.
Bake casserole (uncovered) at 350 degrees for 30-35 minutes, until golden brown on top. Remove dish from oven and transfer to a wire rack. Let it cool and firm up for a few minutes, then slice casserole with sharp knife into 6 equal sized pieces, serve (a spatula works great) and enjoy!
