When buying coconuts, make sure that they are crack-free and have no mould on them. Shake them to make sure that they are heavy with liquid. Now hold a coconut in one hand over a sink and hit it around the centre with the claw end of a hammer or with the blunt side of a heavy cleaver. The coconut should crack and break into two halves. (You could, if you like, collect the liquid in a cup. It is not used in cooking, but you may drink it. I do. I consider it my reward for breaking open the coconut in the first place.) Taste a piece of the coconut to make sure it is sweet and not rancid. Prise off the coconut flesh from the hard shell with a knife. If it proves to be too obstinate, it helps to put the coconut halves, cut side up, directly over a low flame, turning them around now and then so they char slightly. The woody shell contracts and releases the kernel.