Step 1: Preheat oven to 400°F (200°C). Toss cubed butternut squash with 1 tablespoon olive oil, salt, and pepper on a baking sheet. Roast for 25-30 minutes, or until tender and lightly caramelized. Set aside.
Step 2: While the squash roasts, heat the remaining 1 tablespoon olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened and translucent, about 5-7 minutes.
Step 3: Add the minced garlic and grated ginger to the pot. Cook for another minute until fragrant. Stir in the curry powder, turmeric, and cayenne pepper (if using). Cook for 30 seconds, stirring constantly, until fragrant.
Step 4: Add the roasted butternut squash to the pot, along with the vegetable broth and about 3/4 of the can of coconut milk (reserve the remaining 1/4 for the swirl). Bring the mixture to a gentle simmer. Reduce heat to low, cover, and let it simmer for 10-15 minutes, allowing the flavors to meld.
Step 5: Remove the pot from the heat. Carefully use an immersion blender to blend the soup until completely smooth. Alternatively, transfer the soup in batches to a standard blender and blend until smooth (be cautious with hot liquids and vent the lid). Season the soup with additional salt and pepper to taste.
Step 6: Prepare the warm coconut swirl: In a small saucepan, gently heat the reserved coconut milk/cream with the maple syrup or honey (if using) and a tiny pinch of salt over low heat, just until warm. Do not boil.
Step 7: Ladle the hot Curried Butternut Squash Soup into bowls. Drizzle generously with the warm coconut swirl. Garnish with fresh chopped cilantro, if desired, and serve immediately.