yes you can, it's *recommended* if you memorise your essay if you're not confident with cooking up things on the spot, but if you think you know your quotes and themes extremely well (with prior practice adapting quotes and themes to essay questions from past papers) you can do just as well and even better than people who memorised. i knew someone from my grade who memorised quotes and themes the day before and ended up cooking 18-19/20 band 6 essays in the trial [the priority is toward how well you can adapt whatever you have prepared to the fit any question]