A goose egg is the giant among common poultry eggs — two to three times the size of a hen's egg, wrapped in a thick, hard, chalk-white shell and carrying an enormous, deeply orange yolk. Rich, fatty and pronouncedly eggy, it is a seasonal springtime delicacy prized above all by bakers, whose fat-heavy yolks lend extraordinary richness, colour and loft to sponges, custards and pastry. Scarce and costly, it is a treat rather than a staple, laid only for a few months each year.