For the cupcakes:1. Preheat the oven to 350 degrees, and line two cupcake pans with twelve paper baking cups each.2. Sift together the flour, baking powder and salt, and set aside.3. In the bowl of a stand mixer or in a bowl with a handheld electric mixer, cream together the butter and sugar until light and fluffy, approximately 3 to 5 minutes.4. Add the eggs, one at a time, mixing slowly on low speed after each addition.5. Add the vanilla extract to the milk, and set aside.6. Add one third of the flour mixture to the butter mixture, then gradually add one third of the milk mixture, beating slowly until well incorporated. Add another third of the flour mixture, followed by another third of the milk mixture. Stop to scrape down the bowl as needed. Add the remaining flour mixture, followed by the remaining milk mixture, and beat just until combined.7. Divide the batter equally into four smaller bowls. To each bowl, add 1 teaspoon of a different food color, and mix with a spoon until the batter is uniformly colored.8. Then, using a tablespoon, place layers of cupcake batter of different colors in the baking cups. It's okay if your spoonfuls are uneven because this will result in a cool "random" tie-dyed effect. Repeat until all baking cups are two-thirds full.9. Bake for 15 to 18 minutes or until a toothpick inserted into the center of a cupcake comes out clean.10. Let the cupcakes cool on a wire rack for approximately 20 minutes.For the frosting:1. In the bowl of a stand mixer or in a bowl with a handheld electric mixer, mix the butter, sugar, vanilla extract, milk and salt until the frosting is light and airy, approximately 3 to 5 minutes.2. Place the frosting in a piping bag fitted with a large round metal tip. Frost each cupcake with a signature swirl of vanilla buttercream.To make the monster faces:1. Roll out a piece of blue fondant, and using a cookie cutter, cut out a circle with a diameter of 3 inches. Place on top of the frosted cupcake to form the monster's face.2. Using a piping bag fitted with a small round tip, pipe a circle of frosting around the circumference of the blue fondant circle. Pipe two small dots of frosting for the monster's eyes. Pipe another two short linear angled strokes above its eyes to anchor its eyebrows. Pipe one small dot to anchor its nose. Pipe a row of small dots below its nose to represent your monster's teeth.3. Next, decorate your monster's face with candy. Line the circle with jellybeans. Cut two short pieces of black licorice, and place them on top of the linear buttercream strokes to form the monster's eyebrows. Place two tiny candy balls on the white dots of frosting to form the pupils of its eyes. Place a German berry candy on top of the dot of white frosting to form its nose. Serve and enjoy!