Mix together the butter and flour. The mixture will be lumpy.
With a fork, mash the egg yolks and sugar until fine. Add to the flour mixture. Mix everything again. (You can mix by hand or with a dough hook in mixer.)
Shape each cookie into a Hershey’s kisses shape. (If adding walnuts to center, shape cookies into round balls.)
Bake in a preheated oven at 355°F for about 20-25 minutes (or until the cookies are golden in color). Allow cookies to slightly cool.
Combine the powdered sugar and cocoa in a bowl to coat the cookies.
Once cookies have just about cooled, completely coat them in the powdered sugar and cocoa.