Chicken (and/or mushroom) tetrazzini

Our midsouth group is chatting about yummy dishes today, and someone asked for this recipe - I figured I'd put it here and share with everyone else, too! This is a very rich and heavy pasta dish that goes over well at potlucks and big gatherings.

1 onion, diced
4 Tbsp. butter
2 Tbsp. flour
1 package white button mushrooms, sliced (optional)
2 cups milk
1/4 cup sherry (cooking sherry may be substituted if salt isn't an issue)
2 cups cooked, diced or shredded white chicken breast
8 ounces fettucini noodles, cooked al dente, drained and rinsed
3-8 ounce packages provolone cheese, sliced
diced parsley

Place half the noodles in a lightly greased large casserole dish; sprinkle half the chicken on the noodles and set aside.

Saute onion (and mushrooms, if using them) in butter. Once the vegetables are soft, add flour and stir over low heat until it becomes golden and bubbly. Slowly add milk, whisking to keep from getting too lumpy. Add sherry and two packages of provolone cheese (coarsely tear the slices so they'll melt faster.)

When the mixture is thickened and bubbly, remove from heat and pour half over the noodles and chicken. Layer the remaining noodles and chicken; pour rest of sauce over the top. Cover with provolone slices and parsley; bake in preheated 350 oven for 35-40 minutes or until golden brown on top.

(The assembled dish can be refrigerated until baking time, but if you do, keep it covered with foil for the first 20 minutes, and allow at least 10-15 more minutes total bake time.)