Special equipment: a cupcake corer; a pastry bag fitted with a large star tip
For the cupcakes: Preheat the oven to 350 degrees F. Line a cupcake pan with paper liners.
Whisk the flour, baking powder and salt together in a medium bowl.
In a mixer fitted with the paddle attachment, beat the butter and granulated sugar together on medium-high speed until light and fluffy, 1 to 2 minutes. Scrape in the seeds of the vanilla bean and mix to combine. Add the eggs one a time, beating well in between each addition and scraping down the sides of the bowl. Turn the speed to medium and add half of the flour mixture, the milk and then the remainder of the flour mixture, beating in between additions. Do not overmix. Scoop the batter into the lined cupcake pan, using an ice-cream scoop and filling each cup about two-thirds of the way.
Bake, rotating the pan halfway through, until the cupcakes are golden and a tester inserted into the center of a cupcake comes out clean, about 20 minutes. Remove the pan to a rack, cool 5 minutes, and then remove the cupcakes to the rack to cool completely.
For the buttercream frosting: Sift the confectioners' sugar into a medium bowl. In a stand mixer fitted with the paddle attachment, beat the butter on medium-high speed until smooth and light, about 1 minute. Add 5 1/2 cups of the confectioners' sugar and mix on low to combine. Add the vanilla, increase the speed to high and beat until light and fluffy, about 1 to 2 minutes. (Add up to 1/2 cup more confectioners' sugar, depending on how stiff you want the frosting.)
For the decoration: Use a cupcake corer to hollow out the center of each cupcake saving the tops, then fill with a candy ball. Slice the top off of the plug you removed from the cupcake and place back in the hole to seal in the candy ball. Use a couple of drops of purple food coloring to dye three-quarters of your frosting. Fill a pastry bag fitted with a large star tip with the frosting. Dye the remaining frosting with green food coloring and add to a small pastry bag or resealable plastic bag with just a tiny bit of the tip snipped off. Pipe a swirl of purple frosting to cover the top of each cupcake. Place a chocolate wafer cookie on top of each. Using a dab of frosting, wrap the candy belt around the edge of the ice-cream cone. Attach the cone upside-down on top of the cookie, using a bit of frosting to form a hat. Use another dab of frosting to attach the candy-coated chocolates in front for a buckle.