In making sponge cakes, I don’t add any liquid flavoring or citrus zest to the eggs before whipping them because I find the natural oils of these additions retard the full development of foaming and aeration. I add the flavoring either toward the end of whipping the egg foam or into the melted butter, if that is used. Best of all, I like to crush anise or caraway seeds to a fine powder or grate either fresh nutmeg, fresh ginger, or even chocolate and add them to my sponge recipes.
Another essential flavoring, the soaking syrup, is brushed on the cake after it has been baked and just before it is assembled. This is a sugar syrup combined with liquor, liqueur, coffee, tea or fruit juices. It keeps the cake moist for at least a week as well as imparting another dimension of flavor. Some of the cakes in the sponge cake section are so moist and full of flavor that you may feel it is gilding the lily to moisten them any further with dessert syrup.