Preheat the oven to 350°F.
After separating the eggs, place the yolks in a small bowl and set aside. Place the egg whites in a mixing bowl and set aside.
Coat a souffle dish (or dishes) with the butter and set aside.
Place the olive oil in a medium sauce pan over medium high heat.
Add the spinach and cook for about 4 minutes, until the spinach is wilted and most of the water has evaporated.
Add the flour, nutmeg, and salt.
Cook for about one minute until the flour is well incorporated.
Add the milk and cook for about 3 minutes until the sauce begins to thicken.
Use a regular spoon and add about 3 spoons of the spinach sauce to the egg yolks and mix well.
Return the egg yolk mixture to the sauce pan with the spinach, along with the parmesan cheese.
Fold together until the cheese is melted, the mixture is well blended, and the sauce is thick.
Remove from the heat.
While the spinach mixture is cooling, add the cream of tartar to the egg whites and whisk until the egg whites form stiff peaks.
Gently fold the spinach mixture into the egg whites.
Place the mixture in the souffle dishes and place the souffles in the oven.
Bake for 20 minutes and serve immediately.
