Aside from my introduction of ginger, this is a classic shortbread recipe. Because the flavors of butter and ginger are so unadulterated, shortbread is the ideal opportunity to exploit the taste of a fine unsalted European-style butter. The same is true of the ginger. Ground ginger ages rapidly, turning musty after a few months. Buy a small amount of freshly ground ginger at a whole-foods market for a bright sharp flavor. Shortbread will keep for 4 to 5 days in a tightly sealed container at room temperature and up to a month if frozen.