In my experience, few cooking gadgets survive the test of time. The cappuccino frother and smoothie maker loitering in the gadget dungeon of my kitchen pay testament to their usefulness. With this in mind, it was with some scepticism that I slapped a couple of plump chicken breasts on the Giles & Posner Hot Stone Grill. The last time I encountered this “Neolithic” cooking technique was in a little coastal eatery in the Algarve. A fin lab of cow sizzled on a hot stone before my hungry eyes. Having experienced an authentic hot stone in action, I approached Giles &…