For many traders, street food is a means to a more conventional end: you start out selling from the back of a van and, if you amass a big enough following, you might end up with a bricks-and-mortar restaurant. For Ross Gardner and Justin Unsworth, who quit their jobs last year and hit the road as chicken specialists Spit & Roast, joining the street-food revolution was a step in the opposite direction.

Gardner, once an investment banker, had been cheffing for eight years, while Unsworth has been in the catering and hospitality business most of his working life. They met when Gardner joined the kitchen at Medcalf in Clerkenwell, London, which Unsworth co-founded in 2003. "It was fun but stressful. There are so many things that can go wrong in a restaurant," says Gardner. "So we decided to do something much simpler."

Unsworth describes Spit & Roast as his busman's holiday. He sold his share in Medcalf, they turned an old Transit van into a mobile kitchen and started selling at street-food hotspots, including Brockley Market in south London and Kerb in King's Cross. Rotisserie chicken was their speciality but they have since expanded into deep-frying. Now the pair make maybe the finest buttermilk fried chicken in the capital.

"I don't think we appreciate how great it can be," says Unsworth. "We're so steered by bad experiences of fried chicken in the high street. If you buy really good free-range chicken, marinate it overnight and cook it in fresh oil, it's an absolute treat."

Gardner adds: "You could eat it as a nice sit-down meal with sides if someone's gone to the trouble of making mashed potatoes, greens and a good gravy. But it does lend itself to being eaten with fingers and a dollop of hot sauce."

Buttermilk fried chicken

SERVES 4
For the fried chicken
free-range chicken 8 pieces, drumsticks and thighs
salt 2 heaped tbsp
black pepper 2 tbsp
paprika 4 tsp
buttermilk 400ml
plain flour 200g
cornflour 100g
vegetable oil

For the Korean hot sauce
Sriracha sauce (available from supermarkets) 500ml
smooth peanut butter 3 large tbsp
rice wine 1 tbsp
light soy sauce 1 tbsp

Buy your chicken the day before – we use thighs and drumsticks because chicken on the bone tends to have more flavour. Season with half the amounts of salt, pepper and paprika, and cover with buttermilk. This will tenderise the meat and give it a slight tang. Cover with clingfilm and leave in the fridge overnight.

Take the chicken out of the fridge the following day and dredge it. In a large bowl, mix together all the flour and cornflour, and the remaining salt, black pepper and paprika, and dip the chicken pieces in one by one. Scoop some of the flour mixture over the top of each piece and press down with the back of your hand, making sure it's completely coated. Shake off the excess flour over the bowl. When all the pieces have been coated, you're ready to fry.

We use a deep-fat fryer in the van but at home you can shallow-fry in a big frying pan. Fill it with 2.5cm of oil and heat to 150C (it's handy to have a temperature probe to check the heat). You don't want it to go much hotter or the breading will go brown before the meat is cooked. Fry for 10-12 minutes, or until the outside is nicely brown, turning the chicken three or four times. (If you're using a deep-fat fryer, gently nudge the pieces after a few minutes to make sure they're not clumping together.)

Make the hot sauce by mixing all the ingredients together in a bowl. To make sure the chicken pieces are cooked through, heat an oven to 160C/gas mark 3 and cook them on a rack for 10 minutes.

Serve with a dollop of hot sauce. You could also eat this with macaroni cheese or creamy mashed potatoes, with a fennel slaw on the side.