I want to know the answer to the following question:
What ingredient is notably absent from a New Haven-style pizza when ordered plain?
All the background I'm provided with is that "Apizza may be red (with a tomato-based sauce) or white (with a sauce of garlic and olive oil), and pies ordered "plain" are made without the otherwise customary mozzarella cheese (originally smoked mozzarella, known as "scamorza" in Italian).". Is that enough to answer the question?