Slice off the stem end of the pumpkins 1/2 inch from the top, reserving it, scrape out the seeds and the membranes, reserving the seeds for toasting if desired, and brush the inside of the pumpkins with the butter. Top the pumpkins with the reserved stem ends, bake them in a shallow baking pan in the middle of a preheated 375 degree oven for 1 1/2 hours, or until the pulp is tender, and let them cool in the pan until they can be handled. Discard any liquid that may have accumulated in the pumpkins, scoop out the pulp, and in a blender purJe it in batches, transferring it as it is purJed to a large sieve or colander lined with overlapping large coffee filters and set over a large bowl. Cover the surface of the purJe with plastic wrap and let the purJe drain, chilled, overnight.