FOR SOUP: Preheat oven to 350 degrees F. Place squash on baking sheet and bake 30 minutes. Add pears cut side down to baking sheet. Bake until tender, about 30 minutes. Let cool on baking sheet. Scrape flesh (about 5 generous cups) from squash into Dutch oven. Pull skins off pears and cut each half into quarters. Add to Dutch oven.
Meanwhile, melt butter in heavy large skillet over medium heat. Add leeks, curry and thyme. Season with salt and pepper. Saute until softened, about 5 minutes. Sprinkle with sugar and saute 1 minute. Add 1/4 cup broth. Reduce heat to low. Cover and cook, stirring occasionally, until leeks are very soft, about 25 minutes. Uncover and simmer over medium heat until liquid reduces and leeks caramelize, about 5 minutes. Reserve 1/3 (packed) cup leek confit for crab. Add all remaining leek confit and reserved 3 cups broth to squash and pear mixture. Cover and simmer over low heat until pears and squash are very soft, about 25 minutes. Working in batches, puree soup in blender until smooth. Return soup to Dutch oven.
Add cream to soup and rewarm over medium-low heat. Season soup to taste with salt and pepper.
FOR CRAB: Combine all ingredients and reserved 1/3 cup leek confit in medium bowl. Season to taste with salt and white pepper. Cover with plastic and refrigerate.
Ladle 1 cup soup into each of ten large, shallow bowls. Mound crab mixture into each center. Garnish crab with chive sprigs and serve.