With White Rabbit Red Rabbit about to enter its sixth year at the Fringe, Nassim Soleimanpour is riding high. Having premiered at Edinburgh in 2011, the work which involves an actor reading a script blind now numbers thousands of performances around the world, including on Broadway where everyone from Alan Cumming to George Takei have taken part. But this Fringe, the playwright’s fans will also get to see a whole new work from the Berlin-based Iranian.

Famously, Soleimanpour didn’t get to see Rabbit until it had been touring the world for two years with the Iranian government denying him a passport after he refused to do national service. In order to find out what audiences thought of the play, his email address is revealed during the show, inviting people to get in touch. Blank, Soleimanpour’s new play at Summerhall this August, is a direct result of his reception to an outpouring of emotion.

‘One of the main things that really pushed me to write this play was the thousands of emails that I’ve been receiving since 2011, when we opened White Rabbit Red Rabbit,’ he tells me over the phone from Berlin, his new home. ‘In Rabbit, I put my email address in the play and asked the audience members to email me or find me on Facebook. At the time, I didn’t have a clue I’d be under this bombardment of different emails, mostly very kind ones from people all around the globe. That was, and still is, a very deep journey in itself. We’re used to having this play performed simultaneously in different countries and sometimes I wake up in the morning and there are 60 to 70 emails.’

In Blank, Soleimanpour hands the narrative reins to the audience. Each night, a different person will fill in the ‘blanks’ in the script and tell their story. ‘I wanted to find a way to reach more of those stories [from the emails],’ he says. ‘I thought that this was actually my mission now; I owe this to everyone. Rabbit was a very personal story which I sent out into the world. Now I receive thousands of personal stories, from people who have cancer, people who have lost their partners, people who have thought about suicide. So I thought I owed them a story machine. I should design a machine which can be used every time in a room to help this hive-mind share their stories with each other.’

Blank isn’t about putting a chosen audience member on the spot; instead, it’s a joint effort between that person and a performer, to tell a story that’s already been written (their past) and one that’s not yet happened (their future). As a former designer and engineer, structure is very important to Soleimanpour and he constantly refers to Blank as a ‘mechanism’. ‘It’s a very weird machine,’ he explains. ‘I’ve watched it a few time and I’d say I’m happy that it’s built. The type of story being made in Blank is partly true because it’s full of facts from real people. You get a random audience member on stage, and then question this person: what’s your name? Where were you born? What do you do as your profession? These are facts written by this person. I decided to get married to my wife five years ago, and this is writing the story of my life. This is like a kind of collaborative writing.’

It also highlights a process of writing and re-writing that the playwright first noticed in Rabbit, as different actors across the globe added their own personality to his script. ‘There are thousands of actors who did that. I’m always amazed at how spontaneous and creative they are. It took me something like six years to write 40 pages. They could do it in a few hours.’

Despite the huge success of his debut play, Soleimanpour has famously gone on record to say he didn’t like it the first time he saw it. ‘As you can tell, I’m stupidly frank,’ he laughs. ‘The BBC called me and said “what’s your feeling about it?” and I said, “I didn’t like it; I can write a better play”.’

But with this new outing, it looks like Soleimanpour is finally happy. And he’s made peace with his first hit as well. ‘Technically, Blank is way stronger than Rabbit. I feel very confident about Blank, while I’m in love with Rabbit. We are like good close friends. Rabbit helped me and convinced me to write Blank. That’s a good thing. I really owe this play.’

Blank, Summerhall, 8–28 Aug (not 22), 6.30pm, £12 (£10; family ticket £42). Previews 5–7 Aug, £10; White Rabbit Red Rabbit, Assembly George Square Studios, George Square, 6–28 Aug, 4pm, £10–£12. Previews 4 & 5 Aug, £8.