1 1/2-inch round cutter; a pastry bag fitted with tip no. 113; a wooden dowel or thin-handled wooden spoon
For the cupcakes: Preheat the oven to 350 degrees F. Line 18 cups of two 12-cup muffin tins with cupcake liners.
Sift together the flour, cocoa, baking powder, cayenne, baking soda and salt in a medium bowl; set aside.
In the bowl of a stand mixer, cream the granulated sugar and butter until fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition and scraping down the bowl as needed. Beat in the vanilla.
Combine the milk and bourbon in a small bowl. Add the flour mixture to the butter-sugar mixture in 3 additions, alternating with the milk-bourbon mixture in 2 additions. Beat the batter until smooth. Using an ice cream scoop, fill each muffin cup two-thirds full with batter.
Bake until a toothpick inserted into a cupcake comes out clean, 15 to 17 minutes. Let cool completely, about 30 minutes.
For the buttercream frosting: Combine the confectioners' sugar, butter and salt in the bowl of a stand mixer fitted with a paddle attachment. Mix on low speed until mostly incorporated. Add the vanilla, increase the speed to medium high and mix until smooth. Adjust the consistency with milk as desired. Add a drop or two of blue food coloring to the frosting and mix until the desired color is achieved, adding more drops if needed.
For decorating: Roll the yellow gum paste very thin (about 1/8 inch thick or thinner). Using a 1 1/2-inch round cutter, cut 12 rounds from the gum paste.
Elevate a wooden dowel or thin-handled wooden spoon on 2 cans or paper cups with notches cut to hold in place. Drape the gum paste rounds over the dowel to dry and form taco shells, about 30 minutes.
Fill a pastry bag fitted with a leaf tip (no. 113) with the blue buttercream frosting. Starting in the center of each of 12 cupcakes, while spinning the cupcake, pipe the frosting on a flat angle to the top of the cupcake, moving the bag slightly up and down to form a ruffle. Cover the top of each cupcake completely with frosting.
Add the coconut to a small bowl with a few drops of green food coloring. Stir with a fork to distribute the food coloring, adding additional coloring until the desired lettuce color is reached. Snip the red gummy candy into small pieces using kitchen shears to form the tomato salsa. Crumble one of the remaining cupcakes to fine crumbs to form the taco meat.
Assemble the tacos by layering each taco shell with some cupcake crumbs, green coconut and red gummy tomatoes. Finish by grating white chocolate over the top of each for a cheese effect. Place one taco on top of each frosted cupcake.