• Preheat the oven to 350 degrees.  Line a baking sheet with parchment and set aside.

For the cookies

• In the bowl of a stand mixer, combine the softened butter, sugar, and brown sugar.  Cream together until lighter in color and creamy.
  
• Add in the egg, egg yolk, heavy cream and vanilla.  Mix until combined.
  
• Add in the flour, cocoa powder, and baking soda, salt and mix thoroughly.  Stop the machine, scrape down the sides, and mix again. Fold in the milk chocolate chips.
  
• Using a large cookie scooper, divide the cookie dough into 15 equal-sized balls. Use a flat-bottomed drinking cup or glass to press the dough ball into a disc shape and about ½ in thickness.
  
• Bake in the preheated oven for about 10 minutes.  Let cool in the sheet for 5 minutes then transfer to a wire rack. Allow to cool completely before decorating.
  

For the frosting

• In the bowl of a stand mixer, combine the heavy cream, hot cocoa mix, and cocoa powder. 
  
• Whip on medium for about 3-4 minutes or until fluffy and thick.
  
• Transfer the frosting to a piping bag fitted with a large star tip or similar.
  
• Once cookies have cooled, they are ready to decorate.  Starting in the middle of the cookie, pipe a spiral from the center all the way around and stopping just short of the edges.  Repeat with remaining cookies. 
  
• Sprinkle the frosting with the mini dehydrated or regular marshmallows.