2. Melt butter in large saucepan over medium heat. Stir in flour to make smooth paste; cook and stir 2 minutes. Gradually add milk, stirring constantly, until mixture is slightly thickened.
3. Add Cheddar cheese, pepper jack cheese, if desired, and onion to milk mixture. Cook, stirring constantly, until cheese melts. Add broccoli; stir well.
4. Place macaroni in 3-quart casserole. Add cheese mixture; mix well. Sprinkle English muffin pieces evenly over top. Bake 15 to 20 minutes or until muffin pieces are golden brown.