6 T. butter, divided
1 T. olive oil
1/4 c. all-purpose flour
2 c. whole milk, room temperature
1/2 c. heavy whipping cream, room temperature
3/4 c. chicken broth
pinch ground nutmeg
2 1/4 t. salt
1/4 t. freshly ground black pepper
8 oz. white mushrooms, sliced
1 small onion, finely chopped
3 cloves garlic, minced
1 t. dried thyme leaves
1/2 c. dry white wine
6 ounces dried linguine
1/4 c. frozen peas
2 T. chopped fresh Italian parsley leaves
2 c. (15 oz.) larger bite sized cooked chicken (remember it will break down somewhat)
Topping
2/3 c. grated Parmesan
3 T. dried Italian-style breadcrumbs
2 T. butter
Preheat the oven to 350 degrees F.
Spray 8 x 11 x 2-inch baking dish with cooking spray, or use butter.
Melt 3 tablespoons butter in a sauce pan over medium-low heat. Add the flour and whisk for 2 minutes. Whisk in the milk, cream, broth, nutmeg, 1 t. salt, and large pinch of pepper. Increase the heat to medium high, and bring to a boil. Simmer, uncovered, until the sauce thickens slightly (not too much, will thicken more later), whisking often, about 8-10 minutes. Cover and set aside.
Add 1 tablespoon each of butter and oil to medium skillet. Add mushrooms and saute over medium-high heat 2 minutes. Add the shallot, garlic, and thyme, and saute until the shallots are translucent and mushrooms are golden, about 5-7 minutes. Add the wine and simmer until wine evaporates, about 2 minutes. Transfer the mushroom mixture to an extra large mixing bowl.
Meanwhile, bring a large pot of generously salted water to a boil. Break the linguini in half and cook until it is tender but still firm to the bite, stirring occasionally, about 9 minutes. Drain and rinse slightly. Add the linguini, sauce, peas, and parsley to the mushroom mixture. Toss until the sauce coats the pasta and the mixture is well blended. Taste for seasonings. Add chicken and gently mix as not to break up pieces. Transfer the pasta mixture to the prepared baking dish.
Stir the cheese and breadcrumbs in a small bowl to blend. Sprinkle the cheese mixture over the pasta. Drizzle with 2 T. melted butter. Bake, uncovered, until golden brown on top and the sauce bubbles, about 20-25 minutes.
To make ahead, do not add the breadcrumbs/cheese mixture. Place one layer of plastic wrap directly on top of casserole, then cover entire casserole with plastic wrap and refrigerate.
TO REHEAT: Uncover and set casserole on counter for 1 hour to warm slightly. Heat oven to 350 degrees.
Cover casserole tightly with aluminum foil and bake for 1/2 hour, or until casserole is barely warm to the touch.
Remove casserole and increase heat to 450 degrees.
Sprinkle casserole with breadcrumbs/cheese mixture and drizzle with 2 T. melted butter.
Return casserole to oven.
Bake until golden brown on top and sauce bubbles, about 10-25 minutes. Watch closely.
IMPORTANT: Let casserole rest on cooling rack for 15 minutes to set up, or it will be watery. Slice into portion sized squares, and scoop out with a square spatula so the casserole stays together.
NOTE: If you cook mushrooms ahead of time, squeeze out the water with a paper towel.
(Adapted from Giada de Laurentis)
