Cook broccoli just until it becomes tender and is still bright green. Drain well. In pot of boiling water, cook noodles and drain well.
Meanwhile, in medium saucepan, melt butter over medium heat and cook mushrooms for 2 minutes. Blend in flour and cook for 2 minutes longer. Remove from heat and gradually stir in milk. Cook over medium heat, whisking, until sauce is thick and smooth. Stir in sherry, mustard, and salt and pepper to taste. Stir in cooked noodles.
Arrange broccoli in bottom of 6-cup baking dish and place turkey slices on top. Pour sauce with noodles over and sprinkle evenly with Parmesan. Cover with foil and refrigerate.
About 30 minutes before heating, remove casserole from refrigerator and bring to room temperature. Bake, uncovered, in 350°F oven for about 20 minutes or until hot, bubbly and lightly browned. Makes 2 servings.