Cut the chicken into bite-size pieces and mix them with the buttermilk (you should be able to pick up some in most supermarkets; if you can't, you can make your own substitute: stir one tablespoon of lemon juice into 250ml milk, leave it to settle for 10 minutes and you're done) and spices (I like to use jerk spice but anything with a kick will work – mild curry, chilli, paprika, turmeric, garam masala, whatever you’ve got).
Season with salt and leave for six hours; the acid in the buttermilk will tenderise the chicken and allow the spice to penetrate into it.