I've had traditional Tetrazzini made with mushroom or chicken soup and cheddar cheese, but wanted something that says WOW!
My (Italian) husband had never eaten Tetrazzini and said he wouldn't like it, but he not only ate it but went back for seconds. I've made this so many times for family occasions and catering events. It always gets rave reviews because it's so much better than typical Tetrazzini. Substitute turkey during the holidays for an extra special way to use up leftover turkey.
In large stock pot that you will cook the pasta in, dissolve chicken bouillon cubes in water and cook linguine or spaghetti until al dente, about 8 minutes. Drain and set aside, don't rinse.
Salt and pepper both sides of the chicken. In a large heavy skillet or dutch oven, over medium-high heat add the olive oil and brown chicken tender pieces on both sides. Transfer chicken/turkey to platter to cool. (If using cooked turkey, skip this step and melt butter in large skillet.)
Lower heat and to pan drippings add remaining butter, onions, green onions, bell pepper, and celery. (If you're using leftover turkey and have some turkey fat or pan juices left, add about 1/4 cup to the vegetables. Most of the liquid will cook out but the turkey flavor will remain.) Saute slowly, stirring occasionally until they get very soft. Add garlic and saute about 2-3 more minutes. There should be enough butter/liquid remaining to absorb the flour so add more if needed.
To cooked vegetables add flour a little at a time, stirring flour into mixture. Continue adding flour until roux becomes a fairly thick paste, but not chalky. Stir constantly for about 4-5 minutes, making sure flour doesn't stick or turn brown. Gradually whisk in some of the milk until you have a nice creamy, medium consistency. As sauce heats up it will continue to thicken so keep adding milk to maintain a creamy consistency. Remember, this is going to cover the al dente pasta and it will absorb a lot of the moisture so you don't want the final dish coming out too dry.
Add sherry and (optional) mushrooms; simmer on low heat for about 30 minutes or more, stirring frequently. (Note: Do not leave out the Sherry - this is one of the most important ingredients and gives this dish the unique flavor that most Tetrazzini casseroles don't have.) As sauce thickens stir in more milk as needed to keep sauce slightly thick. The more you simmer the sauce the better it becomes but you may have to add more milk occasionally.
Taste and add salt as needed. Don't over salt because the pasta and cheeses will also add salt to the overall dish. While sauce is simmering, cut or break chicken/turkey apart into nice bite size pieces and add to sauce. Cook 15 minutes more. Don't make this dish too salty or spicy. A little cayenne pepper goes a long way and enhances the flavor of the sauce.
Preheat oven to 350, and in large sprayed or buttered casserole dish layer 1/2 of the pasta, 1/2 of the sauce. Top with a nice layer of grated Parmesan, shredded Parmesan and 1 bag of mozzarella or Italian blend cheeses. You want this layer to be the thickest cheese layer so don't skimp. Repeat layers and finish with a thinner layer of grated Parmesan, shredded Parmesan and mozzarella. Bake uncovered for 30-45 minutes until bubbly and cheese begins to turn golden brown.
Serve with buttered or garlic french bread. Enjoy!
This makes a huge pan so recipe can be divided if necessary.