Frozen product. Once defrosted, reheat and consume within 48 hours. You can also microwave from frozen - stir every minute or so and break up any frozen lumps.
Defrost fully, before reheating gently in a saucepan or microwave-safe container, stirring occasionally, till piping hot. As you reheat it, the mash may separate and look lumpy and watery for a time but if you heat it gently in a saucepan, stirring from time to time, then suddenly, magically, it will reassemble itself and be as fluffy and delicious as it was the day it was made.