Preheat oven to 400°F. Lightly grease a baking sheet and place buttercup squash halves cut side down on the pan. Roast until fork tender, about 35-40 minutes.
Meanwhile, place coconut oil in a large pot or Dutch oven over medium heat. Once hot, add onion and sauté until softened, about 5-7 minutes.
Add garlic, ginger and turmeric, stir to combine and cook an additional minute.
Add the red curry paste and spices to the pot, stir until well combined with the onion mixture then add the chopped potato.
Pour the broth into the pot, stir to combine all the ingredients and bring to a boil. Once boiling, cover and reduce heat to a simmer. Cook for about 15 minutes or until potatoes are fork tender.
When squash is finished roasting, remove from the oven and let cool for 5 minutes so you can handle it. Scoop the flesh out of the skin of the squash and add to the soup pot. Stir to combine.
Transfer the soup to a blender in batches and blend until completely smooth (*see note). Alternatively, use an immersion blender in the pot.
Pour the soup back into the pot (if using a blender) and add all but 1/4 cup of the coconut milk and juice of 1/2 a lime. Stir until well combined.
Serve the soup while hot. Drizzle the remaining coconut milk on top of the soup in each bowl and use a spoon or toothpick to swirl it around for a pretty presentation.
Garnish with fresh cilantro, sliced lime wedges and coconut flakes as desired.
Notes
*If using a blender, take care to only fill the canister 1/2 to 2/3 of the way full when blending hot liquids. Start on a slow speed and gradually increase. Cover the top with a kitchen towel in case of any splatters.