1 small pumpkin, cut into large chunks as per photo above (they are usually labelled as "pumpkin pie" pumpkins at the grocery store)
Preheat oven to 375F degrees. Place pumpkin in a baking dish with a lid and fill the bottom with 1/4 inch water. Bake for 35 to 45 minutes until pumpkin is fork tender. Once it's cooked it will easily fall off the skin. You can puree it in a food processor to make it easier to measure the amount needed for the pie.
Alternatively, if you're crunched for time you can buy organic canned pumpkin puree. Of course, roasting it yourself tastes much better is more nutrient-dense.