Filling:

1. Prepare the frosting by creaming together the butter and powdered sugar until smooth.
2. Pour in the heavy cream until incorporated. Filling can be kept refrigerated in a sealed container up to three days.

Cakes:

1. Preheat oven to 350 degrees.
2. Make the cakes by creaming the sugar and butter together until smooth. Add in the egg and mix until incorporated.
3. Next add in baking powder, baking soda, salt and vanilla extract. Mix until well combined.
4. Sift in cocoa powder and mix until combined.
5. Mix in 1/2 of flour and 1/2 the milk, and then mix in second half of flour and then the rest of the milk. Stir until just combined.
6. Scoop out a 1/4 cup of mixture (or use the #16 disher) onto a sheet pan covered in parchment. You can fit 5 scoops on each sheet pan. Bake 18-22 minutes until a toothpick comes out clean from the center.
   
7. Cool on sheet pan and then transfer to a wire rack to finish cooling completely. Store in an air tight container until ready to use.
8. To assemble, spread filling on flat side of one half of the cakes. Top with second half of cake.
9. Sprinkle Mickey Mouse decorettes to sides of whoopie pies.
10. Set any extra frosting aside to attach medallions if making.

Medallions (optional)

1. Melt the white candy melts in a microwave safe container like glass for 30 seconds, stir, and then continue to microwave in short bursts of 15-20 seconds, stirring between times, until fully melted and smooth. Optionally, melt using a double boiler.
2. Next, line 5 standard muffin tins, covering bottoms and all the way up the sides, with cling wrap.
3. Pour in candy melts among the 5 tins, making sure it is evenly distributed.
4. Let set about 30 minutes and then, using the cling wrap, gently remove the discs and set aside.
5. If using a chocolate transfer design, follow the directions on the package and adhere to medallion.
6. Use remaining frosting to add a dot to the top of each assembled whoopie pie and adhere the medallion to the top.