2. Cut the pumpkin in half, scrape out the seeds, and place it, cut-side down, on a baking sheet. Bake for about 40 minutes or until tender and easily pierced with a fork. Allow the pumpkin to cool about 10 minutes before proceeding, as it will be easier to handle when it is not so hot.
3. While the pumpkin is baking, heat the oil in a small saute pan and saute the onion and celery for about 3 minutes or until softened and translucent.
4. Scoop the pumpkin pulp with a large spoon, put it into a large bowl and add the onion, celery, milk and water. Stir to combine. Ladle some of this mixture into a blender and puree it in batches, being careful not to overfill the blender. Strain the soup through a colander to remove any remaining fiber or seeds. Add the lemon juice, cumin, allspice and sherry or Marsala wine. Season to taste with salt and pepper .
5. Spread the pepitas or pumpkin seeds on a baking sheet and roast in the oven for 10 minutes or until toasted.
6. Reheat the soup, divide it among 4 warmed soup bowls and sprinkle with the toasted seeds (pepitas).