In a small bowl, whisk together sour cream, maple syrup, 1 or 2 tablespoons water, and a pinch of salt. Cover; refrigerate.
Melt the butter with olive oil in a dutch oven or large, heavy-bottomed pot. Add onions, apples, ginger and curry powder, and sauté over medium heat until onions are very soft, about 15-20 minutes. Meanwhile, peel the squash with a vegetable peeler, cut in half lengthwise and scrape out the seeds. Chop into roughly 1 inch cubes.
When onions are done, add the stock, squash, and cider and bring to a boil. Reduce heat and simmer until squash is very tender, about 25 minutes. Turn off heat and let cool slightly. Using a stick blender, blend until smooth (or use a regular blender in batches). If soup is too thick, add a little more chicken stock or water. Season with salt and pepper to taste.
To serve, dollop or swirl a spoonful of maple cream on top of each serving.