Butternut Squash Mac and Cheese

Caramelize the Onions - In a large skillet, melt the butter over medium heat. Add the onions in one layer. Reduce heat to medium-low and cook until caramelized, about 25 to 30 minutes. Stir occasionally, keeping the onions in one layer. Reduce heat if browning too quickly.
Cook the Butternut Squash - In a large pot, bring the vegetable stock to a boil. Add the butternut squash and cook until tender, about 7 minutes. Transfer to a blender and reserve the broth.
Puree the Squash - To the blender with squash, add the caramelized onions, milk, salt, and ¼ cup reserved broth. Puree until smooth and creamy. If needed, add up to ¼ cup more broth to thin the sauce.
Cook the Pasta - In a large pot, cook the macaroni in salted boiling water according to the manufacturer's instructions. Drain and leave the pasta in the pot.
Make the Macaroni and Cheese - Pour the butternut squash puree over the cooked noodles in the pot. Add the cheddar cheese and stir until melted and combined. Add more milk if needed to adjust the consistency. Season with salt and pepper to taste.
Toast the Breadcrumbs - In a small pan, toast panko breadcrumbs over medium heat until all sides are golden brown, about 3 minutes. Shake the pan occasionally for even toasting.
To Serve - Serve topped with toasted breadcrumbs and parsley.