Spray a 2 - quart baking dish with Pam (I used a 10 x 13 pan).
Cook pasta in boiling salted water (using the 1/8 teaspoon salt) according to package directions, adding broccoli during last 3 minutes of cooking. Drain and return broccoli and pasta to pot.
In another large saucepan over medium heat melt the butter and add bread crumbs, stirring often or until golden (2 minutes). Remove from heat and transfer crumbs to a small bowl stirring in 1 tablespoon Parmesan. Set aside.
In the same saucepan over medium high heat whisk together the milk and flour until blended and then add in the onion. Bring to a boil and then reduce heat to low and simmer until thickened (2-5 minutes). Remove from heat.
Whisk in the cheese (cheddar and remaining Parmesan) and the rest of the ingredients (mustard - pepper).
Pour pasta and broccoli into prepared pan and cover with cheese sauce; toss to coat.