For cake, preheat oven to 350 degrees F. Grease and lightly flour two 9-inch round cake pans, set aside. (If desired, prepare 13 x 9 pan or 24 cupcakes.).
In a large bowl, with electric mixer on low speed, beat all cake ingredients 30 seconds. Beat on medium speed, scraping sides occasionally, 2 minutes. Pour batter into prepared pans.
Bake 30 minutes or until toothpick inserted in centers comes out clean. On wire rack, cool 10 minutes; remove from pans and cool completely.
For Frosting, in a small bowl, with electric mixer at low speed, beat marshmallow cream, creamy peanut butter and margarine until smooth. Increase speed to medium and beat in remaining ingredients until blended. Evenly spread frosting on completely cooled cake. (Frosting will be sticky.).