Preheat oven to 350°. Combine cola and buttermilk in a 2-cup measuring cup.
Beat butter at low speed with an electric mixer until creamy. Gradually add sugar, beating until blended. Add eggs and vanilla; beat at low speed just until blended.
Combine flour and next 2 ingredients in a medium bowl. Add to butter mixture alternately with cola mixture, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Pour batter into a lightly greased 13- x 9-inch pan.
Bake at 350° for 30 to 35 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes.
Meanwhile, prepare Peanut Butter Frosting. Pour over warm cake. Sprinkle with chopped peanuts.