Hot chocolate cupcakes:

1. Whisk together the hot chocolate powder and hot water. Set aside to cool.
2. In the bowl of a stand mixer, whip the egg and granulated sugar on high until lightened in color and texture (about 20-30 seconds).
3. With the mixer on low, add the vegetable oil, mixing until combined.
4. Stir together the remaining dry ingredients (baking cocoa, flour, salt, baking soda and baking powder) in a bowl and add the remaining wet ingredients (milk and vanilla) to the hot chocolate.
5. With the mixer on low, add the dry ingredients to the egg/sugar/oil mixture in two parts, alternating with the wet ingredients in one part. Mix until just combined to prevent over-mixing.
6. Spoon about 1/4 cup batter into each cupcake liner.
7. Bake at 350F for 18-22 minutes, or until a toothpick inserted in the center comes out with only baked crumbs.
8. Allow to cool in the pan, then move to a cooling rack. Make sure the cupcakes have cooled completely before frosting.

Marshmallow buttercream: 

1. Beat the butter and marshmallow fluff on medium-high until smooth and lightened in color.
2. With the mixer on low, slowly add the powdered sugar.
3. Once the powdered sugar is incorporated, add the vanilla and increase the mixer to high, beating until smooth.
4. Add one tablespoon heavy cream to thin as needed.

Assembly:

1. Spoon the buttercream into a piping bag fitted with a large, round piping tip.
2. Pipe two layers of frosting onto each cupcake.
3. Garnish with half a gingerbread man cookie, sprinkles, and/or bits of chocolate.