Heat oven to 425. In a medium saucepan cook the pasta according to package directions. Add broccoli during last 3 minutes of cooking. Drain pasta mixture. Return to pan; keep warm.
Meanwhile, in large saucepan cook onion in 2 teaspoons of the oil over medium heat for 5 minutes or until tender, stirring occasionally. Remove pan from heat. Add semisoft cheese; stir until cheese is melted and combined.
In a medium bowl whisk together milk and flour until smooth. Add all at once to onion mixture. Cook and stir over medium heat until thickened and bubbly. Reduce heat to low. Stir in cheddar and Asiago cheeses until cheeses are melted. Add cooked pasta mixture; stir to coat.
Transfer pasta mixture to 2-quart casserole. In small bowl combine baguette crumbles and remaining 2 teaspoons oil; sprinkle on pasta mixture. Bake, uncovered, 10-15 minutes or until top is browned. Sprinkle with parsley.
Mac 'N' Cheese Change-Ups:
1. For a fully-loaded protein-packed version, into the basic recipe stir in 1 cup chopped cooked chicken or 1 cup smoked italian turkey sausage.
2. Appeal to grown-up tastes by using smoked cheddar or smoked Gouda instead of Asiago, Gruyere, or Manchego cheese.
3. Stir in southwestern flavor with 1 cup rinsed, drained canned black beans and 1/4 teaspoon habanero sauce or bottled hot pepper sauce. Before serving, sprinkle with fresh snipped cilantro.
4. Add more crunch. After dishing up servings, top with apple slices. Golden Delicious, Granny Smith, or any other variety are all good. For maximum nutrition leave the peel on.