Chicken Tetrazzini

I have a 3-ring notebook in my kitchen where I keep copies of "keeper" recipes which I've tried multiple times with success. This is one of those "keeper" recipes and I make it whenever I've got mushrooms and leftover baked or rotisserie chicken in the fridge. It's classic comfort food.

Chicken Tetrazzini
Yield: Makes 6 servings

2 cups chicken stock (preferably homemade)
3/4 stick (6 tablespoons) unsalted butter
3/4 pound mushrooms, thinly sliced
1/2 teaspoon salt
1/4 teaspoon black pepper
1/2 tsp dried thyme, or one sprig fresh thyme
a pinch of nutmeg
3 tablespoons all-purpose flour
1 cup heavy cream
2 tablespoons medium-dry Sherry (not cooking sherry)
3/4 lb spaghetti or linguine
1 to 1 1/2 pounds shredded cooked chicken
1 ounce freshly grated Parmigiano-Reggiano (1/4 cup)

Put oven rack in middle position and preheat oven to 350°F.  Heat chicken stock in a small saucepan until hot.  Bring a large pot of salted water to a boil.  Butter a shallow 3-quart glass or ceramic baking dish.

Heat 3 tablespoons butter in a large heavy skillet over moderately high heat until foam subsides, then sauté mushrooms with 1/4 teaspoon salt, 1/8 teaspoon pepper, and thyme, stirring, until liquid mushrooms give off is evaporated and mushrooms begin to turn golden, about 8 minutes.

When the pasta water comes to a boil, add the pasta and cook until al dente.

Meanwhile, melt remaining 3 tablespoons butter in a 2- to 3-quart heavy saucepan over low heat, then add flour and whisk while the flour cooks - about 2-3 minutes.  Add warm stock in a fast stream, whisking constantly, and bring to a boil. Reduce heat and simmer, whisking occasionally, 5 minutes. Add cream, sherry, remaining 1/4 teaspoon salt, and remaining 1/8 teaspoon pepper and simmer over low heat, whisking occasionally, 8 minutes.

Pour drained spaghetti, mushrooms, and chicken into the cream sauce and stir to combine.  Transfer to the prepared baking dish.  Sprinkle grated Parmigiano-Reggiano cheese on top.

Bake until sauce is bubbling and top is lightly browned, about 25-30 minutes. Serve immediately.