Most writing advice treats outlining as step one. Alexis Hall, prolific author of Boyfriend Material and Rosaline Palmer Takes the Cake, has described doing it the other way around, letting a draft tell him what the outline needs to contain.

The Direct Answer
He gets an idea and drafts several thousand words first, then goes back to write an outline once he can see what the book actually needs.
Hall has called the method concurrent-yet-iterative, a loop between concept and character that stays flexible well into the writing process.

Draft First, Outline Second

Where a lot of writers plant a flag on one side of the plotter-versus-pantser divide, Hall's actual order of operations sidesteps the question. "I'll get an idea, then I'll sit down and bash out the first X thousand words," he's explained, "and then after that I'll realise that it would be a good idea to have an outline and I'll go back and write one."

Concurrent, Iterative, and Still Flexible

He's described the broader shape of this method as "concurrent-yet-iterative," a loop between concept and character that keeps revising both instead of locking either down early. Structure, in his account, stays genuinely open right up until copyediting starts. He does hold to one fixed rule inside all that flexibility, though: he always writes a book from start to finish, in order, rather than jumping between scenes.

That combination, loose planning but strict sequencing, means his early drafts function less like architecture and more like excavation. He writes first to find out what the book is about, then organizes what he's found. For more on how that fits into his wider approach to craft, see the full Alexis Hall writing routine.

What You Can Steal