I prefer sour cream rather than yogurt. Aren’t they virtually interchangeable? Why specifically is yogurt preferable to sour cream for the Mughlai Chicken?
Nigella's Mughlai Chicken (from FEAST) is her version of the classic Indo-Persian Mughal dish. Mughal dishes were known for their luxurious ingredients and the sauce is made with a combination of almonds and cream, plus yogurt to give a little acidic balance.
Yogurt would have been the traditional ingredient and yogurt appears in many Persian and Turkish dishes. It has a lower fat content than sour cream and the two are not always interchangeable. However, for this particular dish we suspect that you could use sour cream as an alternative to the Greek yogurt (which itself is richer than regular natural/plain yogurt) and add it at the same time as you would the yogurt.