PREHEAT oven to 350° F. Lightly grease and flour 13 x 9-inch baking pan.
PREPARE cake mix batter according to package directions, adding peanut butter before mixing. Pour into prepared pan.
BAKE for 30 to 40 minutes or until wooden pick inserted in center comes out clean. Cool completely in pan on wire rack.
PLACE chopped Baby Ruth and butter in medium, heavy-duty saucepan. Cook over low heat, stirring frequently, until Baby Ruth is melted. Combine evaporated milk, sugar, coconut, peanuts and egg yolks in medium bowl. Add to Baby Ruth mixture. Cook over medium heat, stirring frequently, for about 10 minutes or until thickened. Cool in refrigerator for 30 minutes; stir.
FROST cake with Baby Ruth frosting. Refrigerate cake until ready to serve.