Here is a recipe that uses hard-boiled egg yolks.
I have not made it myself, but listen to the review from the L.A. Times' Food Section:
"New York chef Larry Forgione says that when James Beard first tasted Forgione's strawberry shortcake, the food guru pronounced: "There can be no dessert better, only fancier." After tasting Forgione's shortcake for ourselves, we had to agree. Most of us said we'd never tasted a better shortcake. The secret: hard-boiled egg yolk mixed into the dough. The recipe comes from Forgione's cookbook "An American Place" (William Morrow: 1996, $30), which was chosen as one of our favorite cookbooks of 1996."
Recipe