In a small saucepan, heat the olive oil over medium heat. Add the chopped onion and sauté until onion is tender, about 3-4 minutes. Sprinkle on the curry powder and stir to combine. Cook the onion mixture for an additional minute until warm and fragrant. Add 1/2 cup vegetable broth and cook for an additional 2-3 minutes until onions are softened. Set aside.
In a blender add the leftover roasted vegetables and the remaining broth. Puree until smooth. Add the applesauce and blend again to combine. Add the curried onions and process until smooth. If soup is too thick add a little vegetable broth to thin it out.
Pour the soup into a saucepan and warm over medium heat. Serve.