In a large mixing bowl, combine dry cake mix, 1/2 cup chunky peanut butter, eggs and milk.
Beat with an electric mixer on low speed until combined, scraping sides of bowl often.
Beat for 2 minutes at medium speed.
Spread batter into greased 13 x 9 x 2 inch baking pan.
Bake at 350º for 35 to 45 minutes or until a wooden toothpick inserted near center comes out clean. Cool cake in pan on a wire rack. Make Milk Chocolate Peanut Butter Frosting: In a small bowl, beat together peanut butter and milk chocolate frosting until creamy. Frost cooled cake.