Heat the oven to 400°. Lay a piece of foil or parchment paper on a baking sheet. Spray with vegetable spray and set aside.
Slice the butternut squash in half vertically and scoop out the seeds. Place the two halves of the squash flesh side down on the prepared baking pan and roast for 25-30 minutes or until skin is dark and blistered and flesh is tender and soft. Remove from oven and set aside to cool.
Once the squash is cool enough to handle, scoop out the flesh and transfer to a mini food processor or mash with a potato masher or the back of a fork. Measure out about 1 cup of pureed butternut squash. (A little more or less is ok). Set aside.
IF YOU'RE MAKING THE CASSEROLE VERSION:
Reduce the oven temperature to 375°
MAKE THE BECHAMEL:
In a large saucepan, heat the butter over medium high heat until melted. Sprinkle in the flour and dry mustard, stirring until there's no dry bits left in the pan and it forms a paste. Cook for one minute, stirring constantly until bubbly. Stir in the kosher salt and then add the milk about 1/4 cup at a time, stirring after each addition. For the first 1/2 to 3/4 cup the milk and flour mixture will be very thick -- that's ok ... Continue to add the milk in small additions, stirring until the sauce is smooth before adding more. Bring the sauce to a boil over medium high heat, stirring constantly and scraping the bottom and sides of the pan so nothing sticks. When the sauce starts to bubble, cook for one minute longer, then remove from the heat.
Add the grated cheese and stir until completely melted. Stir in the butternut squash puree to combine. Set aside.
COOK THE PASTA & KALE:
Bring a large pot of water to a boil. Add 1 teaspoon salt. Stir in the elbow macaroni and cook to al dente according to package instructions, stirring occasionally.
When the pasta is about 2 minutes from being done, stir in the kale. Continue to cook until the pasta is al dente. Remove from heat and drain the pasta/kale mixture in a colander.
Transfer the pasta and kale back to the pot and add the butternut squash sauce. Stir to combine. Season to taste with salt and pepper. (Note: this can be served straight from the saucepan at this point or made into a casserole -- Your choice.)
TO MAKE THE CASSEROLE:
Spray a large casserole dish with vegetable spray. Transfer the macaroni mixture to the casserole dish.
Add the bread, parsley and butter to a mini food processor and pulse 6-7 times until you have herb buttered breadcrumbs.
Sprinkle the breadcrumbs over the casserole and bake for 15 minutes to crisp the breadcrumb topping and heat the casserole through. Serve.