|5 T unsalted butter|
|1 T freshly grated Parmesan cheese|
|1 small yellow onion, minced|
|1 10-oz. package frozen spinach, thawed|
|1 1/2 t kosher salt|
|Pinch cayenne pepper|
|3 T flour|
|1 cup milk, scalded|
|4 large egg yolks|
|8 egg whites|
|1/2 cup grated Swiss cheese, divided|
Preheat oven to 400 degrees. Butter a 6 or 8 cup souffle dish with 1 tablespoon softened butter and sprinkle with Parmesan cheese.
Saute onion in 1 tablespoon butter for 2 minutes. Add drained spinach, 1/2 teaspoon salt, and cayenne pepper.
In a medium saucepan combine remaining 3 tablespoons butter and the flour and cook 2 minutes. Stir in milk, 1/2 teaspoon salt, and black pepper. Stirring continuously, cook 2 minutes. Remove from heat and beat in egg yolks, one at a time. Cook an additional 2 minutes over low flame. Fold in spinach mixture.
Beat egg whites with remaining 1/2 teaspoon salt until stiff; fold a quarter of the egg whites into the spinach mixture. Stir in all but 1 tablespoon of the Swiss cheese. Fold in remaining whites and spoon into prepared mold. Top with remaining cheese.
Bake 25 to 30 minutes, or until puffed and golden brown. Serve immediately.