In a large bowl, combine cake mix, milk, eggs, and mix with electric mixer; add vanilla extract at the end. Mix on low for 30 seconds then on high for 2 minutes. Use a spatula to mix well the contents at the bottom of the bowl and on the sides. Add the crushed fiber one bars and mix. Save a little of the crushed mixture until the end. Fill each cupcake liner 3/4 of the way.