Cook pasta according to package directions, cook until "al dente", drain and set aside.
Preheat oven to 350 degrees, have two oval Au Gratin dishes out, and set aside.
In a medium saucepan make Béchamel sauce by melting butter over medium-low heat until melted. Once melted stir in flour and continue to stir until smooth. Increase heat to medium and cook butter and flour mixture until it turns lightly golden, about 5-7 minutes.
While you are doing this, heat the 2 cups of milk in the microwave for two minutes. Then slowly add hot milk to the butter mixture, whisking continuously until smooth and there are no chunks of flour.
Bring to a boil and cook 10 minutes, constantly stirring. Then remove from heat, add in salt, 2 cups of Gruyere cheese, 2 tablespoons parmesan cheese, cooked bacon, and minced onion. Stir until cheese is melted and well combined, then remove from heat.
Add in pasta and gently stir until all of the noodles are completely covered in the cheese sauce.
Pour 1/2 of the noodles in one of the Oval Au Gratin dishes, then the remaining in the second dish.
Top each dish with a 1/2 cup of the Gruyere cheese.
Place in oven and bake for 10 minutes. Then turn oven to a low broil and broil for 5-10 minutes, or until golden and bubbly on top, like pictured.
Let it cool for a few minutes, then serve.