Preheat oven to 350 degrees F. Set up an oven rack into the middle of the oven.
Lightly grease with butter or with cooking spray a 12.25x2.5 baking dish, or a baking dish that would hold at least 7 cups of batter.
In a large bowl, stir and combine all the ingredients until well incorporated. Transfer the batter to the prepared baking dish and level the top with a spatula.
Bake for 45-50 minutes. The casserole is done when the edges are golden brown, the center is settled and it looks puffy, light, and overall done. A toothpick inserted into the center of the casserole should come one clean or with just a few crumbs attached, but no raw batter.
Serve warm garnished with chopped fresh green onion or diced chives.