Heat oil in a Dutch oven over medium heat. Add onion; sauté 4 minutes. Add sweet potato, curry powder, and garlic; sauté 5 minutes. Add green beans, chestnuts, broth, and cannellini beans; bring to a boil. Cover, reduce heat, and simmer 30 minutes or until potatoes are tender, stirring occasionally. Place 4 cups vegetable mixture in a blender; process until smooth. Return pureéd mixture to pan; stir in salt and remaining ingredients. Cook 5 minutes or until thoroughly heated.