Chicken Mac 'n' Cheese

In a large pot of boiling salted water, cook pasta according to package directions until al dente; drain. Heat oven to 350 degrees F. Butter a 3-quart baking dish. In a large skillet, melt butter and add breadcrumbs. Cook over medium heat, stirring until golden and crisp, about 3 minutes. Scrape into a medium bowl and stir in 1/4 cup of the Parmesan cheese and parsley. In a large saucepan, whisk milk, flour, and garlic until flour is blended. Whisking frequently, bring to a boil over medium-high heat. Reduce heat and simmer until mixture is thickened, about 5 minutes. Remove from heat; stir in cheddar cheese, chicken, the remaining Parmesan cheese, mustard, salt, and pepper. Add cooked pasta and cheese sauce to prepared baking dish, stirring well to blend. Sprinkle breadcrumb mixture over top. Bake 35 minutes or until hot and bubbly and crumb topping is golden.