Preheat oven to 325 degrees F. Line cupcake pans with paper liners and set aside.

Combine flour, sugar, cocoa powder, baking soda, baking powder, and salt in a large bowl or stand mixer. Beat on low speed until combined.

Add eggs, buttermilk, water, oil, and vanilla. Beat on low speed until partly incorporated, then scrape bottom and sides of the bowl. Increase speed to medium-high and beat until the mixture is very even and smooth.

Pour batter into cupcake liners, filling each about 2/3 full. Bake for 20-25 minutes, until a toothpick inserted into the center comes out clean. Allow pans to cool on wire racks for about 10 minutes, then remove cupcakes and let cool completely.

To make the frosting, beat the softened butter with an electric mixer on medium speed until creamy. Gradually add the powdered sugar, stopping to scrape down the sides of the bowl as needed. Beat in the vanilla, then the milk. Test the frosting — it should hold a shape well and be fairly stiff.

To decorate ghosts, transfer frosting to a large piping bag or zip-top bag. You can use a large round decorating tip or simply cut off a corner of the bag to make a large hole in the bottom. Pipe frosting on top of cupcakes in large, even circles, starting at the outer edge and working up and in. Pull the piping bag away in one quick, smooth motion when you reach the center top. Decorate with chocolate chips, candy eyes, or other treats as desired. Enjoy!