Preheat oven to 350°F. Grease one 9-inch round cake pan with butter and dust with flour, shaking out any excess. Place a round of parchment in the bottom of the cake pan. Set aside.
In a large mixing bowl, sift together flour, cocoa powder, baking powder, baking soda, and salt. Add in the sugar and whisk the ingredients together. Make a well in the center of the dry ingredients and add the milk, egg, and oil. Using an electric hand mixer, mix the batter together on a low speed until well combined. Pour the batter into the prepared cake pan and place into the oven. Bake for 30 minutes or until a toothpick comes out clean when inserted into the center of the cake. Remove to a cooling rack.
Once cool, remove the cake from the cake pan. Peel the parchment paper off the bottom of the cake and put onto a serving plate.
For the peppermint-marshmallow topping & chocolate ganache
For the Peppermint-Marshmallow: In a medium glass bowl whisk together egg whites, sugar, salt and cream of tartar. Place the bowl over a pot of simmering water and let the mixture cook, whisking occasionally, for 10 minutes or until the sugar dissolves and the mixture becomes fairly warm. Pour the warm mixture into the bowl of a stand mixer fitted with a whisk attachment and whip on high for 10 minutes or until fluffy and has the consistency of marshmallow fluff. Add a drop of peppermint extract and mix until just combined. Taste and add more extract, if needed.
When you’re ready to serve, dollop the marshmallow over top of the cake and spread with an offset spatula, leaving a 1/2-inch border around of the cake. Alternatively, you can put the marshmallow into a piping bag fitted with a star tip to make a festive design.
For the Ganache: Heat the heavy cream in a small saucepan over medium heat. Once the cream is warm, remove the pan from the heat and stir in the chocolate chips mix until smooth.
To serve, pour the warm ganache over top of the cake. Serve immediately. The marshmallow and chocolate will melt together a bit. It’s messy, but fun! For a less messy (but equally fun) serving option, slice the cake, plate individually and then drizzle some ganache over top of the slice.
Grant Melton is an Emmy Award-Winning Producer of the Rachael Ray Show, food writer and recipe developer. He's a contributor to Food52, Food Network Kitchen and Rachael Ray Every Day Magazine. He loves cookies, cocktails and kindness.