preheat oven to 350. combine cola and buttermilk in a 2 cup measuring cup.
beat butter at low speed with ab 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 13x9 inch pan.
bake at 350 for 30-35 minutes or until a wooden pick inserted in the 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.