Bake your cake according to recipe instructions (or package instructions if using mix) and cool completely. Once cooled, crumble the cake into fine pieces, you can do by hand or in processor.
Combine butter, peanut butter, vanilla, and powdered sugar and mix until smooth. Add in the cake crumbs and gently fold into the other ingredients until it all starts to form a dough-like mixture.
Divide the dough into balls (about 1 1/2 tablespoon each) and shape into eggs then place on parchment covered baking sheet or plate. Refridgerate for 1 hour or freeze for at least 30 minutes.
After cooling the eggs, melt chocolate and butter or shortening in a small saucepan or double boiler over low heat. Dip each egg into chocolate and turn to coat all sides before placing it back on the tray. Repeat with all eggs. Allow Chocolate to cool completely then use a thin spatula to loosen from pan. Store in an airtight container. (P.S. these are so good chilled!)
*If you'd like to keep this simpler feel free to use a boxed yellow or vanilla cake mix and cook according to package directions.