Preheat your oven to 375 degrees F. Line two muffin tin pans with paper cupcake liners.
In a large mixing bowl, combine the water, cocoa powder, and espresso powder, and allow it to sit for 5 minutes.
In a medium mixing bowl, whisk together the flour, sugar, baking soda, baking powder, and salt. Set aside.
Whisk in the milk, eggs, and oil into the cooled cocoa mixture. Stir in the flour mixture just until it starts to become smooth.
Use a cookie scoop or spoon to pour the batter into the cupcake pan so each cup is about 3/4 full.
Bake for 20-25 minutes until the tops spring back when pressed down on. Transfer to a cooling rack and allow them to cool completely.
In the bowl of a stand mixer with the paddle attachment (or using a hand mixer), beat the butter on medium speed for 5 minutes until the butter has become light and fluffy.
Turn the speed down to low and slowly add in the powdered sugar and vanilla extract. Add in the milk one tablespoon at a time. Turn the mixer back up to medium speed and mix for an additional 3 minutes.
Divide the buttercream evenly into three separate bowls. Add enough food coloring to each bowl to get a vibrant color. You should end up with one bowl of orange, one bowl of yellow, and one bowl of purple frosting.
Place each buttercream into a piping bag with a large star piping tip.
Sarah Sanderson: On 8 of the cupcakes, pipe one big swirl of the yellow buttercream by placing the piping tip in the middle of the cupcake and adding pressure to the bag. Swirl the frosting around the cupcake, slowly making your way to the top.
Winifred Sanderson: Pipe a large swirl of orange buttercream onto 8 other cupcakes. Then pipe two mini swirls on each side of the big buttercream swirl.
Mary Sanderson: On the 8 cupcakes, start by piping out a swirl of purple buttercream. Then keep piping at an angle while allowing the buttercream to begin to tip over to one side.
Sprinkle the cupcakes with edible glitter.
Store any leftovers in an airtight container in the fridge for up to 3 days.