Make sure your bananas have black spots on them before you peel and freeze them overnight until they are completely frozen.
Place all ingredients in the blender, starting with the pumpkin puree, and blend until smooth.
If you want to use home-made pumpkin puree, use a small sugar-pie pumpkin.
Start by preheating your oven to 400F.
Cut the pumpkin in half with a very sharp knife, and use your spoon to scoop out the seeds, which you can use later.
Place the pumpkin halves, seeded side down, onto a parchment-lined baking sheet.
Cook at 400F for about 40 minutes, or until the pumpkin is very easily pierced with a fork, and is very soft.
Take it out of the oven, lay it on the peel, hold down the peel with a knife, and use your fork to move the flesh away from the peel. This is the easiest method I have found to peel the pumpkin.
Place all pumpkin flesh into a blender, and blend until very smooth.
Be careful when opening the blender, as it can get extremely hot and steamy.