1. Preheat oven to 425 degrees. Lightly butter a 3 quart gratin or baking dish.  Cook pasta. Drain and transfer to a large bowl.

2. Meanwhile, in a large saucepan combine the squash and 2 1/2 cups of the milk over medium high heat.  Bring to boiling.  Reduce to medium and simmer 18 to 20 minutes or until squash is tender when pierced with a fork.  Stir together remaining 1/4 cup milk and flour, stir into squash mixture.  Bring to boiling; cook 2 to 3 minutes or until thickened.  Stir in 1 1/2 cups of the cheese until melted.  Keep warm.

3. Then, in a extra large skillet cook bacon and drain on paper towels.  Crumble.  Pour off all but 2 tablespoons of the greese from the skillet.  Return the skillet to the heat.

4. Add the onions to the skillet.  Cook unil clear.  

5. Add squash cheese mixture, onions, and bacon to bowl with pasta.  Toss well and transfer to prepared baking dish.

6. Place bread in the food processor.  Pulse to form large bread crumbs.  Transfer to a small bowl- mix with melted butter.  Sprinkle the remaining cheese and bread crumbs over the mac and cheese.  Bake for 14 to 15 minutes or until the top is golden brown.  Cool 5 minutes.  Sprinkle with parsley