Roast butternut squash.
Remove peel and seeds and cut down in small dice—about 1/3” cubes.
If boiling, peel butternut squash.
Cut in large 2-3” chunks and bring to a boil with water.
Boil until done—about 15-20 minutes.
Drain.
Dice in 1/3” cubes like above.
Meanwhile, bring water to a boil in large stock pot.
Add pasta and cook until al dente.
Drain and set aside.
In a saucepan on top of the stove over medium heat, melt 2 tbsp. of the butter.
Add onions and sauté a few minutes.
Whisk in flour and continue whisking and sautéing about 2 more minutes.
Add cream slowly—about 1/8 to ¼ cup at a time and continue whisking until all the cream is added and no lumps remain.
Reduce heat to low and add salt, pepper and nutmeg.
Allow mixture to thicken before removing from heat.
Add Monterey Jack cheese and stir to combine.
Add drained pasta and stir to combine.
Add cubed butternut squash and stir very gently to combine so butternut squash maintains its shape.
Spray an 8x12” glass baking dish with cooking spray.
Pour macaroni mixture into casserole dish.
Melt remaining 1 tbsp. butter.
Stir in panko bread crumbs.
Sprinkle bread crumbs over top of casserole.
Bake at 375° about 30 minutes or until heated through and lightly browned on top.