Wipe the spatchcocked chicken with kitchen towels. Rub the skin and the exposed underside with salt, place on a rack in a roasting tin and set in the fridge for 8-10 hours.
The next day, make the masala paste by grinding all the ingredients without using any water.
Gently push small amounts of the masala paste under the skin to cover the entire chicken. Smear some on the underside of the chicken as well. Let it sit in the fridge for 2 hours.
Preheat the oven to 230℃.
Make a paste with olive oil, baking powder and a little salt (if required) and brush all over the chicken.
Roast the chicken , skin side up on a wire rack placed in a roasting tin, for 45 minutes.
Test the chicken for doneness by inserting a kitchen thermometer into the thigh and breast. The temperature should be 65℃ or higher. Take the chicken out, let it rest for 15-20 minutes before carving and serving.