Cook and drain pasta according to package directions. Slice the mushrooms 1/8 of an inch thick and sauté in 2-3 tablespoons of the butter, along with sliced onion, and chopped garlic until lightly browned. Combine the remaining butter with flour and add chicken broth, stirring over low heat until thickened. Add the cream, salt, pepper, sherry, and garlic powder.

Divide the sauce in half. And one half of the chicken meat, and half of the mushrooms and cooked pasta. Butter a casserole dish and turn the pasta mixture into the casserole leaving a well in the center of the pasta.

Turn remaining cooked chicken half into the center of the pasta mixture. Top with Parmesan cheese, and bake uncovered at 400°F for 20 minutes.

Optional: may also top with butter to breadcrumbs and grated cheddar or American cheese.