6tbspunsalted butter, plus extra to grease the baking dish
1/4cupparmesan cheese, finely grated
6tbspall purpose flour
2cupswhole milk
1/2tspkosher salt
1/2tspfreshly ground pepper
5extra large eggscan use 6 large eggs
2 1/2cupsGruyère, grated plus three slices for garnish, optional
3tbspchives, minced
Instructions
Preheat oven to 400 degrees.
Butter a 5 to 6 cup gratin dish. Sprinkle have of the parmesan into the dish, rotating it until the bottom and sides are coated.
Heat a saucepan over medium heat and melt the butter.
Add the flour and mix well with a whisk until it has fully absorbed the butter and is free of lumps. Cook it for an additional 10 seconds.
Pour in the milk while continuously whisking. Keep whisking until the béchamel sauce has come to a boil and thickened. Allow it to cook for an additional 2 minutes after that.
Remove from the heat and allow it to cool enough to handle.
Add the eggs to a bowl and break the yolks with a fork and then beat them well.
When the béchamel has cooled, quickly whisk in the eggs, salt, pepper, Gruyère cheese, and chives.
Pour into the prepared gratin dish. Sprinkle the other half of the parmesan cheese over the top. If adding, top with the 3 slices of Gruyère cheese.
Bake for 40 minutes or until it has puffed up and the top is deeply browned.
It will remain inflated for a while but is best served immediately.