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.

PEANUT BUTTER FROSTING

1/4 cup butter

3/4 cup milk

1 cup creamy peanut butter

1 (16-oz.) package powdered sugar

1 teaspoon vanilla extract

Melt butter in a large saucepan over medium heat. Whisk in milk, and bring to a boil, whisking constantly. Reduce heat to low, and whisk in peanut butter until smooth. Gradually whisk in sugar until smooth; remove from heat, and whisk in vanilla. Use immediately.