Lightly butter 9-inch cast-iron pan or soufflé dish. Preheat oven to 375°F.
In medium pot, heat oil over medium heat. Add jalapeños and onions, and cook until slightly softened.
Add milk and bring to simmer. Once simmering, slowly whisk in cornmeal. Once cornmeal is thickened, reduce heat to low and cook for 4 minutes, stirring frequently. Remove from heat.
Whisk egg whites until light and airy.
Transfer cornmeal mixture to medium bowl. Stir in egg yolks, corn, sausage and Cheddar. Season with salt and pepper.
Fold in egg whites until just combined.
Pour into prepared dish and cook for 15 to 25 minutes, or until browned and set.
Garnish with sliced green onions to serve.