Add egg yolks to a stand mixer with the whisk attachment. On the highest speed whisk yolks until they thicken and are lighter in color, about 3-4 minutes.
Meanwhile, in a medium saucepan over medium heat warm up ½ cup heavy cream.Add a splash of the warm cream to the whisked egg yolks and stir gently. (We are shocking the eggs so they don't get too hot too fast and scramble.)Add the eggs with the rest of the milk into the saucepan. Cook mixture until thickened, 2 minutes, stir constantly.
Take off of the heat and stir in chocolate until melted.
Meanwhile, add the remaining ½ cup of heavy cream to the stand mixer with the whisk attachment. Whisk until cream forms soft peaks, 2-3 minutes.
Very carefully fold the whipped heavy cream into the chocolate mixture. Divide the chocolate mousse between two bowls or glasses. You could also make 4 smaller portions if you prefer.Place in the refrigerator for 2-3 hours to set.
Before serving top with the peppermint whipped cream and your choice of topping. Some of my favorites include: Mint Oreos, Andes Mint Candies, Chocolate Shavings, or Candy Canes.
Peppermint Whipped Cream
Add cream and sugar to a stand mixer with the whisk attachment. Whisk until cream forms soft peaks 2-3 minutes. Add in a couple drops of peppermint extract or more to taste. Serve on top of the chocolate mousse.