Shortbread cookies can be made with or without egg yolks. Egg yolks interact with shortbread ingredients to make the cookies sturdier with a tender texture. They also add a subtle flavor component to shortbread.
Simplest Shortbread
Basic shortbread dough consists of flour, butter and sugar. This recipe turns out rich, buttery, crispy, crumbly cookies. Without egg yolks, these cookies tend to spread and lack well-defined edges.
Baking Chemistry
Egg yolks act as emulsifiers to bind the fat, flour and sugar in shortbread dough. The protein in egg yolks provides structure to the dough and the fat adds flavor. Egg yolks act as tenderizers in shortbread dough. Yolks do not provide much leavening, which is desirable for shortbread dough.
The Role of Egg Yolks
Shortbread made without egg yolks are crisp, but crumbly. An egg yolk gives the cookies a finer texture, and cut-out cookie shapes have cleaner edges. A whole egg, however, makes the dough sticky and difficult to work with and results in tougher shortbread.