Heat oven to 375° F/171°C. Grease and line a baking sheet. Set aside.
In a bowl, mix butter, shortening, egg yolks and vanilla, then blend–in cake mix until well incorporated. The result will be more like dough than a cake batter.
Chill for about 15 minutes for easier handling.
Roll out the dough and cut into desired shapes and place on the prepared baking sheet.
Bake for 10 to 15 minutes or until golden.
Cool cookies slightly before removing from the baking sheet. Serve
Notes
Yield: 10-15 cookies, depending on the size of the cutter