Cut the acorn squash in half and remove the seeds. Place the squash into a baking dish, cut side down. Add enough water to cover the bottom 1/2 inch of the pan.
Cook the squash in a 350°F oven for about 45 minutes, or until tender when poked with a fork. When the squash is cool enough to handle, remove and discard the skins.
In a medium-sized pot, sauté the onions in butter over medium heat until they become translucent.
Add allspice, cardamom, white pepper, and salt, and stir until the spices become fragrant. Add chicken broth and cooked squash, and cook until heated through.
Use either a stick blender or a regular blender to puree the soup until smooth. Return the soup to the pot, and add the heavy cream. Heat through, and avoid boiling after the cream has been added.
Garnish with pumpkin seeds and cilantro to serve.
Recipe Tips
When using a standard blender rather than an immersion blender, fill it no more than halfway with hot soup and hold the lid down firmly with a folded kitchen towel before blending. Hot liquids expand when blended and can cause the lid to blow off. Blend in small batches and work carefully.
To get a smoother texture, push the pureed soup through a fine-mesh strainer before adding the cream. This step is optional but eliminates any remaining fibrous bits for an exceptionally silky result.
If the soup is thicker than you'd like after blending, stir in a splash of additional chicken broth until you reach your preferred consistency. The thickness of the squash flesh varies from one squash to the next, so some adjustment is normal.
For a deeper, more caramelized flavor, roast the squash at 400 degrees F for 35 to 40 minutes instead. At the higher temperature, the cut side will pick up more color and the natural sugars will caramelize more aggressively, producing a noticeably richer, nuttier base.