Preheat your oven to 350 degrees F. Grease a baking sheet or line it with a Sil-Pat.
In a bowl, stir together the hot water an cocoa powder until smooth. Set aside to cool.
In a medium mixing bowl, combine the flour, baking powder, baking soda, and salt.
In a large mixing bowl, beat together the shortening and sugar until well combine and smooth.
Add in the egg and vanilla. Mix to combine. Add the flour mixture, and beat until just about combined. Add the cocoa mixture and milk and beat until smooth, scraping the bowl as needed.
Portion the batter using a small cookie scoop (or rounded tablespoonfuls) onto your prepared baking sheet about 2 inches apart. (I got 12 portions on a jelly roll pan.)
Bake for 10 to 12 minutes or until the tops are firm.
Remove from the oven and transfer to a wire rack to cool completely.
In a large mixing bowl beat together the shortening, sugar, marshmallow fluff, and vanilla until well combined.
If you want to give your some color, now is the time. Add a few drops of red gel food coloring and mix until evenly colored. Add more food coloring as needed until your desired color is reached.
Flip half of the whoopie pies upside down.
Use a medium cookie scoop to portion 2 heaping tablespoons of filling on the bottom side of the upside down whoopie pies. Spread the filling evenly over the cookie towards the edges.
Place each of the top halves of the whoopie pies on a baking sheet. One at a time, place the 2 skewers over the middle of the cookie top with a little space between them. Set the circular cutter just above the top skewer, to the right of center, and press down gently until it just begins to cut into the cookie. While holding the skewers in place (It helps to have a second person holding them) spray the top of the cookie with the silver food color. Just lightly coat it, don't go all crazy!
Remove the skewers and the fondant cutter. You now have a Death Star. Repeat with the remaining cookie tops.
Gently place each of the Death Star tops on the filling, decorated side up, and press down until the filling reaches the edges of the cookie.
Take a bite and come over to the Dark Side.
You can leave the filling it's natural white color and this concept would still totally work. I did red since the Dark Side light sabers are red.If you're not up for decorating the tops, these are still killer, classic whoopie pies and SO so good!