Making butternut squash puree is so easy, and it freezes well. I made some puree today for a butternut squash ravioli I plan to make later on. If that recipe turns out well, I'll do it again and freeze it for the winter.
To make butternut squash puree, I essentially follow the same method I use when I made fresh pumpkin puree. Preheat your oven to 350 degrees. Scoop out the seedy and stringy part of your squash. Place them face down in the pan, and add a little water. Bake for about an hour, or until the flesh is soft. Allow to cool for 10-15 minutes then scoop it out. I use a handheld blender, but you could use a standard blender.