Preheat the oven to 350℉.
Cut the squash in half lengthwise and scoop out seeds and guts with a spoon, making sure to clean the flesh until all stringy fibers have been removed.
Place the squash halves on a lined baking sheet, brush the (extra) melted butter on the flesh, and season slightly with salt and pepper.
Flip the squash flesh-side down and roast in the preheated oven for 35 minutes.
Remove from the oven, flip the squash over (flesh-side up) and return to the oven for an additional 15 minutes. While roasting, mix together the cinnamon and sugar and divide the butter into four pats.
Remove the squash and sprinkle with the cinnamon sugar, dividing it between the four squash halves. Add a pat of butter in the hollow of each squash and return to the oven, switching to broil, for 5 more minutes.
Serve immediately in the shell and mix some of the seasonings butter and squash flesh with a fork before taking a bite.