Prepare the souffle dishes; liberally coat two 1-cup souffle dishes or ovenproof ramekins or custard dishes with butter on the bottom and sides of the dish, and then sprinkle with the 2 tablespoons of cheese. Set aside on a baking sheet. If you don’t have souffle dishes you can use an ovenproof 8-inch skillet and prepare in the same way.
Preheat the oven to 375 degrees.
Separate the 3 eggs, cracking the yolks into a small bowl and the whites into a large bowl. Add the extra egg white to the other three whites in the bowl and set aside.
If using fresh spinach, heat the oil in a medium skillet over medium-high heat. Add the spinach, salt and pepper to taste and cook, stirring for about 4 minutes or until thoroughly wilted. Cool slightly and chop; set aside. You’ll need ½ cup packed spinach; set aside. If using frozen spinach, place in a microwave-safe bowl and microwave for about 2 minutes until softened. You can also place frozen spinach in a small pot of simmering water for about 2 minutes; drain. Squeeze dry with paper towels.
In a medium saucepan, heat the 2 tablespoons butter over medium-low heat. When sizzling, add the flour and stir to create a smooth paste and cook for 2 minutes. Add milk and cream and whisk until smooth and slightly thickened, about 3 minutes. Whisk in the spinach, ¾ cup cheese, egg yolks, salt and pepper and nutmeg. Cook for 1 minute. Remove from heat.
Whip egg whites until firm peaks form. Fold the whipped whites into the spinach mixture with a soft spatula until fully combined. Divide the mixture between the two prepared souffle dishes or place in the 8-inch skillet. Place on the baking sheet and place on the middle shelf of the preheated oven. Bake for 30 minutes, or until the souffles have risen and are golden brown and don’t appear to be wet. Serve immediately.