WHAT is your favourite economy trick with food? Perhaps its a pet recipe. Perhaps it's a method of cooking to make food go farther and taste better. The Ministry of Food wants your cooking secrets Whatever it is send it to the Ministry of Food. The country needs ideas like yours to help other housewives score yet another wartime food victory. Our address is The Ministry of Food, London, S.W.1. So yield up those cherished secrets. Meanwhile, here are ideas and recipes other women have sent to help YOU get the best out of the nation's larder.