Snow-Day Pasta Casserole by cucinagirl

9 oz penne pasta 
11 oz chicken-breast (about 2 medium) 
6oz  frozen spinach* (thawed, excess moisture squeezed out) 
6oz frozen peas 
4oz freshly grated sharp cheddar* 
2 oz freshly grated parmesan  
2 tablespoons butter 
1/4 cup flour 
2 cups hot milk (preferably whole or 2%) 
garlic powder 
(white) pepper 
cayenne pepper

*Feel free to substitute whatever vegetables and cheeses you like. 

Preheat oven to 350F.

Heat about a teaspoon of olive oil in a nonstick skillet.  Cut chicken into bite-size pieces, season with salt, pepper and garlic powder and sauté over medium heat until cooked through (about 5 minutes).  Set aside.

Meanwhile, bring a 4-qt pot of water to boil.  Generously salt the water and add pasta.  Cook until pasta it is not quite al dente (about a minute less than the package instructions).  Drain and return to pot.  (If the pasta takes 10 minutes to cook, you can add it to the water just before adding the milk to the béchamel—see below.)

The Béchamel

In a 2-qt sauce pan, gently melt butter.  When butter is melted, add flour, whisking constantly until a smooth paste is formed.  Cook, whisking, about 2-3 minutes over medium heat.  Mixture should begin to have a nutty, toasted smell.  Add hot milk, whisking constantly.  Bring mixture to a simmer and cook, stirring constantly, until thick (3-5 minutes).  Add seasoning to taste.  (Several dashes of salt, pepper, and garlic powder, a couple dashes of nutmeg, and a couple pinches of cayenne pepper.) 

Turn off the heat.  Add about half each of the cheddar and parmesan and stir until melted and smooth.  (At this point, it actually becomes sauce mornay, which is simply béchamel with cheese.) 

Add the sauce, chicken, and vegetables to the pasta and fold gently until combined. 

Pour mixture into a 9” x 13” casserole, smooth and top with remaining cheese.

Bake for 20 minutes on rack in the middle of the oven, until edges are bubbly.   Adjust rack closer to the top and broil on high for about 5 minutes (watch it carefully!) until the cheese just begins to brown.

Allow to cool about 10 minutes before serving.