Preheat the oven to 350°F (175°C).
Slice each acorn squash in half lengthwise. Scoop out the seeds and stringy fibers using a spoon until the flesh is smooth and clean.
Place the squash halves cut side up on a parchment-lined baking sheet. Brush the flesh with melted butter and season lightly with salt and pepper.
Flip the squash halves cut side down and roast for 35 minutes.
Remove from the oven, flip the squash flesh side up, and return to the oven for another 15 minutes.
While they roast, mix together the cinnamon and sugar, and divide the remaining butter into four small pats.
Once roasting is complete, sprinkle each squash half with the cinnamon-sugar mixture. Place one pat of butter in the center of each half.
Switch the oven to broil and return the squash for 5 more minutes, just until the butter and sugar melt into the flesh.
Serve immediately, in the shell. Stir the butter, sugar, and soft squash together with a fork before eating.
