Place the squash, cream, stock, and salt and pepper into a saucepan and cook over medium heat, until the squash is mushy and tender, about 25 minutes. Puree this mixture until very smooth with an immersion blender or in a food processor.
In the last 15 minutes of the sauce cooking time, add the spaghetti to the rapidly boiling water stirring occationally, remembering to add a small palmful of salt to the rapidly boiling water beforehand.
When the pasta is cooked al dente, drain it and place it back in the pasta pot, add one ladleful of the cooking water then pour the squash mixture over the spaghetti, tossing very slightly, only to coat. Serve with a sprinkling of grated Parmesan cheese.