What Will An Extra Egg Yolk Do To Your Chocolate Chip Cookies?

If you're experimenting with chocolate chip cookie dough, you're probably playing around with every ingredient except for the eggs and flour, the foundation of it all. There are countless baking hacks that range from browning the butter, adding walnuts like the famous Levain Bakery recipe, or even sprinkling flakey salt on the melted chocolate for another layer of flavor. According to Serious Eats, however, the secret to upgrading your chocolate chip cookies lies in the eggs, specifically the egg yolks. 

Because egg yolks contain lecithin and fat, they enrich both the flavor and texture of chocolate chip cookies. If you prefer your cookies light and chewy rather than dense or crispy, adding egg yolks to your dough won't disappoint. For best results, Serious Eats recommends adding one extra yolk per whole egg the recipe calls for. Balance here is important, because too much egg yolk will incorporate too much moisture, rendering your batch spongy and cakelike rather than the texture of a traditional cookie.

Why do egg yolks make chocolate chip cookies softer?

Eggs are one of the most important ingredients in any baked good recipe, but contrary to popular belief, their function isn't solely to bind all the ingredients together. That's why substituting eggs for other common binders, such as applesauce or chia seeds, doesn't produce exactly the same results. 

Life Made Sweet explains that before the dough even gets baked, the egg is already altering its structure by shortening the gluten strands in it. The egg also acts as an emulsifier, lending itself to creamier dough that's tender when baked. These effects, however, are entirely due to the properties of the yolk, not the white, Life Made Sweet points out. The egg white, instead, has a natural drying effect. Typically this is counteracted only by the addition of sugar, but if you want your cookies to be even more moist and soft, just one extra yolk can do wonders.