In large pot or Dutch oven, heat oil over medium high heat. Add celery, carrot, and onion, and cook, stirring frequently, until onions are translucent and vegetables are beginning to soften, 3-5 minutes. Add sweet potatoes, rice, and curry powder. Stir to combine. Sprinkle with salt and pepper. Cook, stirring occasionally, until rice grains are translucent, 3-4 minutes. Pour in vegetable broth. Bring to a boil. Cover and reduce to a simmer. Cook until rice is tender and sweet potatoes are softened, 35 to 50 minutes. Season to taste with salt and pepper.
If you prefer a chunky soup, serve immediately. You can also partially puree with an immersion blender, or transfer 2 cups of soup to a regular blender, puree until smooth and stir back into soup. Serve hot with maple syrup drizzled on top.