So in the actual HSC, the essay is only on your prescribed text, and that's it.
However, for people who have started Year 12 this year, your first assessment will be a comparative essay, where on top of your prescribed text, you will need to find a related text (often in a different form) to the original.
Unless you're getting confused with Module A, where you will go through 2 texts side by side (could be the same or different form)