In the belly of the squash (where you scooped the seeds out of) put a 1tsp of butter, a sprinkle of brown sugar, and a good dollop of maple syrup (there is NO WRONG WAY to do this...it's entirely up to you and the flavor you want, also how many extra calories you want to add).
Place the squash halves on a cookie sheet (you might want to line it with foil or parchment to make your clean up easier) and bake for about 45-50 minutes on 375*. Depending on the size of the squash it could take longer (or shorter). You want the squash to be soft and to be able to scrape it out of the shell. Voila! It's done!
I usually figure a 1/2 an acorn per person, and depending on the size of the butternut squash a 1/4 per person.