Hilary Mantel won the Man Booker Prize for her novel Wolf Hall in 2009. She won the Man Booker once again in 2012 for the sequel Bring Up the Bodies. In a Fresh Air interview, she talks about her technique

I make up as little as possible. I spend a great deal of time on research, on finding all the available accounts of a scene or incident, finding out all the background details and the biographies of the people involved there, and I try to run up all the accounts side by side to see where the contradictions are, and to look where things have gone missing. And it’s really in the gaps, the erasures, that I think the novelist can best go to work, because inevitably in history, in any period, we know a lot about what happened, but we may be far hazier on why it happened. And there’s always the question: Why did it happen the way it did? Where was the turning point? Every scene I go into, I’m looking for these contradictions, antagonisms, turning points, and I’m trying to find out the dramatic structure of history, if you like.[Mantel Takes Up Betrayal, Beheadings In ‘Bodies’]

You can listen to the entire interview on this page. In Guardian, she explains how she wrote Wolf Hall

After I had written the first page I was flooded by exhilaration. I am usually protective of my work, not showing it to anyone until it has been redrafted and polished. But I would have liked to walk around with an idiot grin, saying to the world: “Do you want to see my first page?” Soon the complexity of the material began to unfold. So many interpretations, so many choices, so much detail to be sifted, so much material: but then, suddenly, no material, only history’s silences, erasures. Until a late stage, what would become a trilogy was still one book. It was only when I began to explore the contest between Thomas Cromwell and Thomas More that I realised I was writing the climax of a novel, not merely another chapter. The facts of history are plain enough, but the shape of the drama was late to emerge, and the triple structure later still. In my mind, the trilogy remains one long project, with its flickering patterns of light and dark, its mirrors and shadows. What I wanted to create is a story that reflects but never repeats, a sense of history listening and talking to itself.[Hilary Mantel: how I came to write Wolf Hall]