The recipe doesn't call for extra steps, such as folding in egg whites or using extra egg yolks, so it comes together pretty quickly. (sunnysideupsd.com)
Then add in the egg, extra egg yolk and vanilla and continue beating until evenly combined (about 30 more seconds). (justsotasty.com)
Therefore, to ensure our cookies stay soft we're adding in an extra egg yolk for tenderness. (justsotasty.com)