The cheese sauce for this classic recipe uses skim milk and 2 percent sharp cheddar cheese to make a low-fat meal in less than 30 minutes.
Heat large pot of lightly salted water to boiling. Add pasta and cook 6 minutes. Add broccoli and cook an additional 4 minutes. Drain.
Meanwhile, whisk milk and flour together in a small saucepan. Bring to a simmer over medium heat, then simmer 3 minutes, until thickened. Remove from heat and whisk in mustard, salt, pepper and cayenne.
Add grated Cheddar, whisking constantly until melted. Transfer pasta and broccoli to serving bowl. Pour cheese sauce over pasta-broccoli mixture and stir until coated.