Lecithin

Liquid lecithin, available in health food stores, is a soy derivative (but it is also found in egg yolks) and acts as an emulsifier in butter cake batter. It makes cakes slightly higher and moister and adds a subtle, sweet aftertaste, but it also slightly dulls the buttery flavor. I recommend using it if you are making a butter layer cake 3 to 4 days in advance of serving. To the eggs, add ½ teaspoon per 2 to 2½ cups flour/7 to 8.7 ounces/200 to 250 grams. Be sure to store the lecithin in the refrigerator because it is highly prone to rancidity; if it has an off smell, discard it.