Step 1Heat the oven to 375 degrees. Lay the squash cut side down on a foil-lined baking sheet. Place the garlic cloves on a double thickness of foil and drizzle with oil. Fold the foil into a packet around the garlic and lay it on the baking sheet. Bake until both squash and garlic are very soft and the squash is caramelized, about 1 hour. Let stand until cool enough to handle.
Step 2Scrape the squash pulp into a soup pot. Squeeze the garlic out of the skins into the pot.
Step 3Shake the can of coconut milk well and pour the contents into the pot. Add 1 can cold water. Bring the soup to a simmer and cook, stirring occasionally, 15 minutes.
Step 4Cool slightly. Transfer the mixture to a blender, working in batches, and puree until smooth. Wipe the pot clean and return the soup to it.
Step 5Add the curry paste, starting with 1 teaspoon and working up to desired heat. Simmer until warmed through. Season with salt to taste. Add the lime juice to taste. Serve garnished with either Thai basil, cilantro or scallions. Makes 5 1/2 cups.