Assemble acorn squash on a baking sheet. Place 1 tablespoon of butter and brown sugar in each half. Add 1/4 teaspoon of nutmeg in each and season with salt. Bake until golden and tender, about 1 hour to 1 hour 15 minutes, basting flesh of squash several times.
Twenty minutes before the squash is done, sprinkle edges with raw sugar. Serve squash warm.