When planning to make your own puree, it’s best made with a Sugar pumpkin, not a Jack ‘O Lantern/Halloween pumpkin. Sugar pumpkins have a lot more flavour and are not watery when cooked.
Cut your pumpkin in half, scoop out the seeds and stringy bits (a ice-cream scoop works well), place cut sides down on a parchment lined rimmed baking sheet and bake in a preheated 350 F oven for 1 hour, check by inserting a skewer, it should be very soft. Cool, scoop out the pumpkin flesh and puree in a food processor.
If you are using the puree in baking, make sure it’s very dry. I recommend placing the puree in a fine sieve and letting as much moisture as possible drain out for a few hours or cover, place in the fridge overnight.