I was stuck with essay writing like a month ago as well.
How I copped with it.

I sat down to write an essay.
I didn't had the information.
That implies that during writing, I had many confusions and questions.
Noted down all those confusions and questions.
And then searched for answers to those confusions and questions.
And that systematically lead me to write a normal sized essay.

This is my strategy. Feel free to suggest better strategies.