Two months ago Nick Roberts received an 'on this day' message on his Facebook wall, and it reminded him how little time it had taken to throw together 2014's first edition of Electric Fields with his brother Alex. Back then, it was a modest, thousand-capacity one-day festival headlined by popular local names Fatherson and We Were Promised Jetpacks – yet within two years it had become five times the size and added another day, featuring decent-sized headliners in the Charlatans and Primal Scream, and a strong, expansive, supporting lineup.

In a Scottish festivals scene shrunk by the absence of T in the Park but otherwise holding its own, Electric Fields is the undeniable breakout success of the last couple of years. This summer, the task is to build on the success of the two-day format, and the organisers have once again chosen popular, commercial headliners in Frightened Rabbit and Dizzee Rascal, with a strong undercurrent of good quality local and international artists in support; The Jesus and Mary Chain, Kate Tempest, Band of Horses, Arab Strap, British Sea Power and Anna Meredith are notable among an eclectic bunch.

'We started out as a result of going to a lot of different festivals around Europe and down south,' says Nick now, 'and realising that among all of Scotland's great festivals, there was no smaller event which sat comfortably in a commercial position and wasn't ashamed of that. We wanted to put on the kind of bands you might get at Latitude, Green Man or End of the Road, but in Scotland.' The first year was an experiment, the second was an attempt to repeat the experiment's success (King Creosote and The Phantom Band headlined), and 2016 was where things turned a corner.

This upturn in fortunes came with the addition of new promoting partners – Paul Cardow from PCL in Glasgow, and Andy Smith and Ben Robinson from Kendal Calling and Bluedot – who just clicked with the Roberts'. 'It was pretty great to have new partners involved with business sense, but who were willing to keep the event small and grow it sustainably,' says Roberts. At the same time, the previous year's move by T in the Park from its long-established site and the closure of the nearby Wickerman after the tragic death of its owner opened up the need for an event like Electric Fields.

'We've also seen the demise of Rock Ness and the Connect festival only operating for a couple of years,' says Roberts. 'We have to build that confidence again, to convince people that we really do intend to stick around.' As to why the new Electric Fields has hit the ground running, he has one simple explanation. 'When I looked over last year's sales I realised the average age of those attending was 33. That seemed really old, until I realised that it's me and my brother – it's a festival put together by people who know what they want, and who know what people their age want from a festival.'

For Electric Fields, that's a combination of a strong lineup which it's easy to make a positive decision about, family-friendliness (already, 500 of the tickets sold for 2017 are for under-17s) and a bunch of good-quality extras beyond the music. Roberts points to the fact that Leith's exceptional food market The Pitt will be making an appearance this year, as well as bar-quality cocktails and the like. 'It's common to hear people saying the festival market is saturated right now, and that's kind of true,' he says. 'So it's about stripping it right back to "if you like the sound of this, you'll get exactly what you've paid for" – you can be assured you'll be spending two days with good people who are there for the right reasons. I think we've had something like three arrests in three years.' Personally, he's looking forward to Frightened Rabbit, because he says he's of an age where they've been with him since his teens ('Scott Hutchison came up to me at Record Store Day to say thanks – apparently this is their first headline slot at a Scottish festival'), and Band of Horses. And then there's Dizzee Rascal. 'It's a tricky one, deciding who to finish the festival with on Saturday night, but we realised that a good festival's like a wedding – you start off with the ceilidh, but by the end you want to put a tie around your head and have a disco. He's still a great artist, but it shows we're not taking ourselves too seriously. For me, though, the fact the rest of the bill isn't filler is the most important thing; it's filled with up-and-coming acts who are really well thought of by us.'

For the future, Electric Fields is looking at the possibility of getting larger or possibly expanding to three days, but anything they do won't come at the cost of breaking the 'promise' they feel they have with their audience. 'We won't jump from 5000 to 25,000 in a year,' says Roberts. 'It's about making sure our audience trust us at each stage … we're on a nice site and we care about what we do, so there are always opportunities, but we have no mad desire to reinvent the wheel too quickly.'

Electric Fields, Drumlanrig Castle, Dumfries and Galloway, Fri 1 & Sat 2 Sep.