Heat the oil in a large saucepan over medium heat. Add the garlic and onion and cook, stirring, for 5 minutes or until soft. Add the pumpkin and corn and cook for 3 minutes. Add the stock and bring to the boil. Season with basil and black pepper.
Reduce the heat to medium-low and simmer, uncovered, for 15 minutes or until the pumpkin is tender. Remove from the heat and blend or process soup with the yogurt and nutmeg, in batches, until smooth. Reheat in saucepan, if necessary.