Carefully cut pumpkins in half. Place 2 pumpkin halves on a microwave-safe plate and cook on high power for 8 minutes, or until soft-enough to work with. You will have to do this in 2 batches. Allow pumpkin to cool.
Remove the seeds and stringy innards. (Note: you can save the seeds to roast later.)
Scoop out the pumpkin pulp and place in a large mixing bowl. Add the remaining ingredients – except for the butter. Mix until combined.
Preheat oven to 350°F. Lightly grease a 9”x13” casserole dish.
Place the pumpkin mixture evenly in the casserole dish. Dot the top with little pieces of butter. Cover with foil.
Bake in the preheated oven for 45 minutes – 1 hour.