Use a sharp paring knife to make several slits around the squash. This will let the steam escape.
Place squash in a microwave safe dish or on parchment paper in the microwave. Cook on high for 15 - 25 minutes. Halfway through, turn squash over and test for doneness. Squash should be soft and easily pierced with a paring knife. Time will vary depending upon the strength of your microwave and how big your squash is.
Allow squash to cool until safe to handle. Cut lengthwise, scoop out pulp and seeds, and discard. Scoop out the squash flesh, scraping against the skin, and place in a bowl. Set aside.
Use a mortar and pestle or spice grinder to ground up the cloves, cardamom pods, and peppercorns. Set aside.
In a large pot over medium high heat, heat the butter. Add the white onion and cook soft, about 3 - 5 minutes. Season with salt. Next, add the garlic, ginger, and spices. Cook until fragrant, about 1 - 2 minutes.
Next, add your squash and broth, and then bring to a bowl. Cover and reduce heat to a simmer. Let simmer for about 5 minutes and all the squash is very soft.
Use an immersion blender to blend in the pot. Or scoop out small batches to blend in a regular blender. Blend until smooth and return back to your large pot.
Return the soup to the heat, on medium low. Taste for seasoning and adjust as needed. and Next, add a can of coconut milk. Allow to heat up for a few minutes.