Melt butter in a large pan on medium/high heat. Add flour and whisk until just combined and slightly browned.
Slowly add heavy cream, ⅓ cup at a time whisking in between. Reduce heat to medium.
Add spices and whisk to combine. Add 3 cups of cheese, one handful at a time while stirring continuously. Remove from heat and set aside.
Cook pasta according to the package instructions until just al dente. Turn off heat and add spinach to blanche. Drain and add to cheese sauce.
Pour mixture into a 9”x13” baking dish. Sprinkle the remaining 1 cup of cheese. Cover with foil and bake for 20 minutes. Remove foil and broil for 2 minutes or until the top is bubbling and browned.
