I've been making my own pumpkin puree for a few years now using this method. I've recently discovered a much easier way to do it! Cutting squash is hard work and always seems a bit dangerous. Instead cook the pumpkin (or try other squash) whole, and then cut it. I usually cook two pumpkins at once.
Wash and dry pumpkin. Place one drop of olive oil into palm of hands, then rub hands onto dry pumpkin. Place pumpkin on a foil covered sheet into a 350° oven; do not poke or pierce with a knife. Bake for one to two hours, depending on size of the pumpkin. You'll know it's ready when the pumpkin is slightly browned, dents easily with a wooden spoon, and there is a pumpkin aroma filling the kitchen. Remove from oven and let cool for 10-15 minutes. Cut in half with a serrated knife. Remove and discard seeds (or save them for roasting) and stringy center. Now scoop the flesh from the skin and put into a large bowl. Whip with an electric mixer or immersion blender until smooth. Refrigerate or freeze until needed.