1In bowl, mash bananas and add banana flavoring and 1t sugar. Mash altogether. set aside.
In large bowl, mix the dry cake mix and dry pudding mix together. Add the ingredients listed on the back of the cake box and add 1 cup of buttermilk with them. Add the banana mixture. Beat together until well mixed.
Pour in a greased 9x13 and bake in preheated 350 degree oven for 45-55 minutes, depending on oven.
Meanwhile, in bowl, mix the frosting, peanut butter and 1/2 cup powdered sugar. Use a little milk if it's too dry. But, my frosting usually isn't. Depends on the peanut butter. Frost cake when cooled.
Note: You can use a chocolate frosting for a peanut butter cup frosting. Goes good with banana as well.