I never remember my essays because I go point blank as soon as I read the question and ask myself "did the essay I memorised tie in with the question or do I have to change the structure AGAIN? FML!". I recommend remembering key quotations/evidence and the arguments, points, case studies, language techniques, author's POV etc that surrounds that particular quote. I find doing that a lot easier; I've been doing that my whole Preliminary, HSC and University life and it works - just chuck in the paragraphs that fits the question and make sure the quotes answer the question.
EDIT: Which ever method of memorising the essay you take - just make sure that you're able to do it and that it will help you in the long run.