I went to Uni when I was in my mid 30s, having not even bothered writing essays at school! This was how I fell into working:
Did all the reading/thinking/chatting with other students. I kept an A4 plastic envelop with me and when I had a thought about the essay I scribbled it down and shoved it in the envelope. If I came up with a good description or great sentence, I scribbled it down and it went in the envelope. Everything that came up that was relevant went in the envelope. (Meanwhile, I'd be doing the reading etc for the next essay - we'd have 3 or 4 a term to do.)
At some point in this notes time when my main focus was on another topic, an essay shape would surface which would be shoved in the envelope.
When I was close to deadline - a few days, say - I would start editing'; go through all the notes and sort them into relevant paragraphs according to the vague essay plan I have. By this time, I'd have a lot of the essay held in my head. Sometimes I was lucky enough that it would almost write itself, as if I'd just got it in my head and my brain was connected directly to the tip of my biro bypassing my consciousness altogether! That didn't happen that often though, so don't despair. I'd already done quite a lot of the background subconsciously so it did mean I didn't need a huge amount of time actually getting it onto paper.
My dd's essay plans re so detailed that she might as well have written the essay in my view,, so I know my essay plans would never have passed muster. They were always very sketchy with just headings I guess and the occasional bit of detail that I might otherwise have forgotten - never more than a word or two per heading anyway.
If you can get the bulk of the thinking done some weeks before it's due and move onto another thing, you'll find that it stews in the back of your mind and you'll get hte odd bit of carrot bubbling up to the surface which you scribble down and forget until you need to look at it for writing.
I found it also meant that so long as I'd done the background work, that essays in exams were easy to write.
Does any of that make sense. I've just written off the top of my head and not done any editing at all.