Preheat oven to 375 degrees F (190 degrees C). Butter one 8x8x2- inch glass baking dish.
Whisk milk, cornmeal, and salt in a heavy saucepan over medium heat. Bring mixture to a boil, whisking constantly until mixture begins to thicken, about 4 minutes. Reduce heat to low and cook until the mixture is very thick, stirring frequently, about 20 minutes.
Transfer cornmeal to a large bowl. Stir in corn, green onions, and butter. Add the egg yolks one at a time, stirring after each one.
Beat the egg whites until stiff peaks form. Fold half of the egg white mixture into the warm cornmeal to lighten it; fold in remaining egg whites. Spread the batter evenly in the prepared pan.
Bake in preheated oven until light, puffed and golden brown, about 30 minutes. Serve immediately.