First prepare the cashews for the cashew cream. In a small bowl combine cashews and water. Set aside. Allow to soak for at least 1 hour.
Place a rack in the center and upper third of the oven and preheat oven to 400 degrees F. Lightly drizzle two baking sheets with olive oil. Set aside.
Slice pumpkins in half. Use a spoon to scrape out all of the seeds and strings. The seeds can be rinsed and saved for roasting. Discard the guts and strings.
Place pumpkins so that the scraped flesh is face up. Drizzle each half with olive oil, salt, and crushed red pepper flakes. Place in the oven and allow to roast until soft and a fork inserted through the flesh meets no resistance, about 30-40 minutes.
Remove from the oven and allow to rest until cool enough to handle. Once cool enough to handle, scoop soft pumpkin flesh out of the pumpkin skin, measuring 4 cups into a medium bowl. Set side.
In a large pot, heat olive oil over medium heat. Add onions and cook until browned and translucent, about 7 minutes. Add garlic and cook for one minute more. Add curry powder and cook for one minute more. Add 4 cups of pumpkin flesh and stir until incorporated. Add vegetable broth and stir to combine. Bring soup to a boil and simmer for 20 minutes. Remove from heat and use an immersion blender to blend the soup until creamy. (If you don't have an immersion blender, you can add the soup to a blender and blend until smooth. This can be done in several batches.)
Lastly make the cashew cream. In a blender combine cashews and its soaking water. Blend until smooth, about 1 minute. Add cashew cream to the blended pumpkin soup. Stir to combine.
Add salt and pepper to taste.
Serve warm with a drizzle of olive oil and fried sage leaves.