2/3 cup shortening
2/3 cup white sugar
1 cup milk
4 egg yolks
3 teaspoons vanilla extract
2 (9 inch) prepared chocolate cake mix
Preheat oven to 375º F (190º C). Lightly grease a lightly floured 9x13 inch baking pan. Line cake mix-sheets with foil.
In a large bowl combine butter, sugar and milk. beat at medium speed until mixture is light and fluffy.
Divide batter evenly between prepared pan and prepared sheet pan. Bake in the preheated oven for 60 minutes, until a toothpick inserted into center of the cake comes out clean. Allow to cool in pan on wire rack for 1 hour.