Here's what that looks like:
∙ Write a bunch of little paragraphs with random thoughts on a topic.
∙ Organize them into topics and sections.
∙ Once the structure is clear, I create an outline.
Or, as @paulg once wrote: "Expect 80% of the ideas in an essay to happen after you start writing it, and 50% of those you start with to be wrong."
The frustration you feel is a good thing. It means you're thinking thoughts you've never thought before, which is proof of progress.
Then, once you've exhausted your ideas, create an outline