Instructions:
Preheat oven to 375°F (190°C) and grease a 9×13 inch (23x33cm) baking dish with nonstick spray.
Place the onions in a saucepan and add water just to cover. Bring to a boil, reduce the heat and simmer for 8 minutes. Drain and toss the onion slices with the butter.
In a large bowl, whisk together the eggs and evaporated milk. Add cooked onions, cracker crumbs, cheese, salt and pepper. Stir to mix.
Transfer the mixture to the prepared baking dish.
For the filling, combine cracker crumbs and melted butter. Sprinkle over the casserole.
Bake until center is set and top is golden brown, about 45 minutes.
Remarks
To make this recipe vegetarian, you can replace the soft butter with vegetable butter. This casserole can be served as a side dish or as a main dish for a vegetarian meal.
If you want to add more flavor to the dish, you can try adding diced bacon or ham to the onion mixture before cooking.
This casserole can be made ahead and stored in the refrigerator for up to 3 days. Simply reheat it in a 350°F oven until piping hot.