In a large pot, boil butternut squash, until soft and tender. Strain and remove from heat, let cool.
Mash butternut squash with a potato masher. Season with salt and pepper.
In a skillet on medium-low heat, add 2 Tbsp butter, add onions sauté until golden brown, stirring occasionally. Remove from skillet.
In same skillet on medium-low heat, add 4 tbsp. Butter, sprinkle flour and whisk for 2 minutes to make a thin paste, then add cream, whisk until thickened for 2 minutes.
Place on low heat, add mashed butternut squash, when heated add cheddar cheese. If sauce is thick add a splash of cream. Constantly stirring until sauce is hot. Add in Onions and, test and season with salt.
Add 2 Tbsp. Melted Butter and breadcrumbs in a bowl, mix well.
In an oven dish, add butternut cream sauce, cooked pasta, and remaining butternut squash cream sauce, mix until combined.
Sprinkle breadcrumb mixture on Butternut Squash pasta, place in oven at 375 degrees for 15 minutes, until golden brown. Remove from heat and ready to serve.