How can you not love the combo of peanut butter and marshmallow cream, yum. I saw this site linked from my fav blog Slashfood
See note on filling
Note: For the filling, I simply used a few heaping tablespoons of marshmallow fluff and sprinkled it with 1/3 cup of peanut butter chips. If I were to make this cake again, I would add powdered sugar to the marshmallow to increase it's viscosity. Without the addition of sugar, the marshmallow will leak out from between the cake layers and from the peanut butter frosting.
Cake:In a large bowl, beat butter and sugar for about 5 minutes, until light and fluffy. Stir together flour, baking powder and salt. Set aside. Combine egg whites, milk and vanilla extract. Add 1/3 of the flour mixture to the butter mixture then add half the milk mixture. Continue to alternate, beginning and ending with flour mixture.
Pour the batter into two greased and floured 9 inch round cake pans and smooth top with spatula. Bake cakes about 25 to 30 minutes, or until a toothpick inserted in the center emerges clean.
Cool in pan on rack for 5 minutes, then turn out onto a rack and let cool completely.
Frosting: In an electric mixer cream together the butter and peanut butter until smooth and fully incorporated. Add the powdered sugar a cup at a time and use milk to adjust the consistency to your liking.
Put cream in the center.
Frost the cake liberally and sprinkle the top with additional peanut butter chips.