Turkey Tetrazzini is a fancy name for a turkey casserole with a cream sauce, mushrooms, and peas, and we've always used it for a leftover dish after Thanksgiving when turkey is so abundant. But, the truth is, it's great anytime you have some leftover turkey or chicken. Turkey Tetrazzini can taste slightly bland so my version includes some garlic, bacon, and herbs to punch up the the flavor of the sauce. Dare I say, "BAM?"
Preheat the oven to 375 degrees.
Bring a large pot of salted water to a boil over high heat. Add the pasta and cook until al dente. Drain well and set aside.
Melt 4 tablespoons of the butter in a large ovenproof casserole dish over medium heat. Sauté the onions until they start to become translucent, for 5-6 minutes. Add the garlic and sauté for 2 more minutes. Add the mushrooms, herbes de Provence, and 2 tablespoons of the butter, and cook until the liquid has evaporated, about 6-8 minutes. Remove from pan and set aside.
Sprinkle the flour over the mixture in the pan and reduce the heat to low, stirring constantly for 2-3 minutes to cook off the flour taste. Stir in the broth and the wine.
Bring to a simmer and cook over medium-low heat for about 2 minutes. Gradually stir in the half-and-half and cook until thickened, stirring constantly until mixture coats the back of wooden spoon, for 5 minutes.
Combine the pasta, sauce, onions and mushrooms, turkey, peas, and bacon in the casserole. Stir in 2/3 cup of the Parmesan cheese. Season with salt and pepper, to taste.
In a small bowl, combine the remaining Parmesan and the breadcrumbs. Season with salt and pepper, to taste.
Sprinkle the mixture evenly over the Turkey Tetrazzini, and dot the top with the remaining butter, cut into small pieces. Bake until the top is golden brown, for 30-40 minutes.