Besides deviled eggs and chopped salads, I rarely think of adding hard-boiled egg yolks to recipes, much less baked goods, but it turns out that doing so can give cakes, shortbreads, and biscuits the most tender crumb imaginable.
Photo by Anthony Tong Lee.
According to Bon Appetit, adding sieved, hard-cooked yolks to a cake or biscuit recipe keeps everything nice and tender by disrupting the gluten network:
What happens is this: The tiny bits of cooked yolk intersperse throughout the batter and get in the way of the gluten network that forms when flour mixes with wet ingredients. Gluten is necessary in baked goods to give them structure, but too much makes for a tough, chewy crumb that's generally undesirable in the pastry world.
Obviously, this means that you don't want to add any yolks to chewy baguettes or pizza crusts, but this tip is perfect for buttery cakes, biscuits, cornbread, or anything else in which a moist, crumbly texture is desired. It's also startlingly easy to execute. Just sieve up a yolk or two, and stir 'em in; no other adjustments to the recipe are needed.