This savory egg and cheese puff is more akin to a pudding than a soufflé, so don't dismay when it loses some of its height.
Preheat oven to 375 degrees F. Coat a 3-quart souffle dish or similar baking dish with cooking spray.
Bring milk and scallions to a simmer in a heavy medium saucepan over medium heat. Whisking constantly, slowly sprinkle in cornmeal. Cook, whisking constantly, until mixture has thickened, about 5 minutes. Remove from heat and let cool for 10 minutes. Whisk in egg yolks, Parmesan, Cheddar, 1/2 teaspoon salt and pepper.
About 45 minutes before serving, beat the 7 egg whites and remaining 1/2 teaspoon salt in a large mixing bowl with an electric mixer on high speed until soft peaks form. Whisk one-fourth of the beaten whites into the cornmeal mixture. With a rubber spatula, fold in remaining whites. Spoon batter into the prepared baking dish and smooth the top.
Bake the puff until puffed and golden brown, 30 to 35 minutes. Serve immediately.
Make Ahead Tip: Prepare through Step 2, cover and refrigerate for up to 2 days. Return to room temperature before continuing.
1 starch, 1 high-fat meat