Spinach Souffle (Basic)

Why I Love This Recipe
You can very easily use any cheese that blows your hair back, instead of Cheddar in this recipe.
Ingredients You'll Need
10 oz package spinach (Thawed, and squeezed of excess water)
1/4 cup butter
1/4 cup AP Flour
1 cup Whole Milk
1/2 tsp Kosher Salt
1/8 tsp Ground Black Pepper
1/8 tsp Dry Mustard
1 cup Shredded Sharp Cheddar (Or Gruyere, Emmental, Havarti, Gouda)
4 egg yolks
5 egg whites
1/4 tsp Cream of Tarter
Finely grated Parmagiano-Reggiano
Directions
Preheat oven to 375.
Grease a 2 qt souffle dish with butter sprinkle with Parmagiano; This helps the souffle climb up the side of the dish.
In a small bowl, lightly beat egg yolks.
Melt butter in a medium sauce pan;
In a small bowl, combine flour, salt, mustard and pepper.
Add to melted butter and cook roux until golen brown.
Slowly add milk while whishing constantly, continue cooking while whisking until thick.
Add shredded cheese and stir until melted.
Condition yolks with 1/2 cup of Mornay sauce.
Add to the sauce pan and cook for 1 more minute, whisking constantly.
Stir in thawed spinach.
Set aside to cool slightly.
In another bowl, beat egg whites until frothy, add 1/4 tsp cream of tarter and continue to beat till firm peaks (a little past soft but not stiff)
Fold whites into the spinach mixture and pour into your souffle dish.
Bake for 30 minutes or until a knife inserted in the center comes out clean.