Q: What is shortbread?
I don't think I've ever met anyone who doesn't like shortbread. You'd have to dislike butter to not like shortbread, and well, who doesn't like butter!?
Shortbread gets its name from its main ingredient - lots and lots of butter. That's because fat has the remarkable ability to shorten the texture of baked goods, making them more tender and crumbly. On a food chemistry level, fat coats gluten protein precursor molecules (glutenin and gliadin), preventing them from cross-linking, forming a network of long gluten strands and ultimately developing a tough, elastic texture. This process is referred to as shortening since the fat generally shortens the protein strands.
Shortbread differs from a sugar cookie in that it contains no eggs and it is unleavened, meaning that it does not contain baking powder or baking soda. It is made primarily of butter, sugar and flour. This lends a rich flavour and dense, yet tender crumb. The lack of eggs in this recipe also contributes to its crumbly texture, since eggs typically provide cohesiveness in baked goods.
In this shortbread recipe for Orange Herbed Shortbread, I combine orange with the piney, citrusy notes of rosemary and the musty, earthiness of thyme. The pieces of (homemade) candied orange peel provide a pleasant textural contrast as well.