Preheat oven to 375. Line cupcake pan with 12 liners.
Process or pulse Fiber One cereal in a food processor or blender until fine, like powdered Parmesan cheese. Set into a glass bowl, blending together the dry ingredients: salt, baking soda, baking powder, flour, and Fiber One mix. Then sift ingredients. (very important for light fluffy cupcake!)
In a KitchenAid or mixing bowl, mix together sugars, oil, egg, and molasses until completely blended, about 2-3 min. Add in vanilla extract and maple flavoring, mix another 30 seconds.
With your mixer on low, alternate the buttermilk and dry ingredients. Add 1/4 of the dry mix, 1/3 of the butter milk, 1/4 of the dry mix, 1/3 of the buttermilk, 1/4 of the dry mix, the remainder of the buttermilk, and the remainder of the dry mix.
The batter will be thick. Using a small ice cream scoop to ensure even scoops, distribute batter into the cupcake pan. Bake for 18-22 minutes or until a toothpick comes out clean when a cupcake is pierced.
Let cupcakes cool completely.
For frosting, melt one stick of unsalted butter over medium heat, whisking constantly. Keep a close watch on the mix. When butter begins to turn brown, remove from heat, whisk together, and let butter cool to room temperature.
Once butter is cool, move to stand mixer or mixing bowl. Add vanilla and salt, and blend. Then add the powdered sugar slowly with your mixer on slow. Then slowly add the prune juice and mix on medium speed until a frosting-like consistency is reached. It may need a little more or less than 1/4 of a cup depending on how thick your mixture is.
Use an offset spatula to frost cupcakes. Top with Fiber One if desired.