Which of the following ingredients is essential for making cheesecake, including NY style?

Cream cheese is the key ingredient in making cheesecake, particularly in New York style cheesecake. This style is known for its dense, creamy texture, which is primarily achieved through the use of cream cheese. The fat content and the texture of cream cheese provide the rich flavor and structure needed for a traditional cheesecake.

While other ingredients, such as eggs and sour cream, play supportive roles in achieving the right consistency and flavor, they cannot replace the fundamental role that cream cheese serves in defining the classic cheesecake. Ricotta, although sometimes used in certain cheesecake variations, does not contribute to the characteristic texture that is expected in a New York style cheesecake. Therefore, cream cheese is essential for the recipe, making it the correct answer.