Heat oil and melt the butter in a large pot over medium heat. Cook and stir the onion in the butter and oil until tender.

Mix the carrots ans squash into the pot. Pour in vegetable stock, and season with salt, pepper, and nutmeg. Bring to a boil, reduce heat, and simmer until vegetables are tender.

In a blender or food processor, puree the soup mixture until smooth. Return to the pot, and stir in the heavy cream. Heat through, but do not boil. Serve warm with a dash nutmeg.