Before mixing the ingredients, preheat your oven to 175 °C (350 °F) and then use some cooking spray to coat a large baking dish.
Spread half (3 ½ ounces/1 can) of the whole green chile peppers evenly at the bottom of the greased baking dish.
Top the pepper’s layer with half (4 ounces) of the Monterey Jack cheese and Cheddar cheese.
Sprinkle with the remaining whole green chile peppers and set aside.
Now break two large eggs into a medium mixing bowl and beat them using a whisk until they are watery and foamy.
Whisk in 5 ounces of evaporated milk, and 2 tablespoons of all-purpose flour.
Sprinkle with ¼ teaspoon of salt and continue mixing until it forms a rich topping.
Now drizzle this flour-egg mixture over the top of the green chile peppers.
Place the baking dish in the pre-heated oven and bake for 20 to 25 minutes or until it is light brown on the edges.
Take out the baking dish from the oven and gently pour 8 ounces of tomato sauce evenly over the top.
Set the baking dish back in oven and bake for another 12 to 15 minutes.
Finally remove the dish from oven and place your Chili Rellenos Casserole on a large serving plate.
Sprinkle it with the remaining Cheddar and Jack cheese and serve warm.