Whip the heavy whipping cream in a bowl until medium stiff peaks form. Chill in the fridge until needed.
Melt the chocolate and peppermint baking chips in a heat proof bowl set over a pot of barely simmering water. Stir until melted and smooth. Remove from heat.
In another heat proof bowl, whisk together the egg, egg yolks, and sugar, until a pale yellow. Place the bowl over a pot of barely simmering water and continue beating until mixture is warm to the touch. (scrape down the sides of the bowl as necessary)
Remove the bowl from the heat and continue beating until the mixture comes off of the whisk in thick ribbons and had cooled to room temperature. Slowly fold in melted chocolate into the egg mixture until it’s well combined.
Get the whipped cream and fold about 1/2 of the whipped cream into the chocolate mixture to lighten it. Then fold in the remaining whipped cream, being careful not to over beat it. Over beating can cause it to loose its volume. Pipe into Joli cups leaving a few of inches to decorate the tops then chill for at least an hour.
Crown the mousse with a dollop of whipped cream or sprinkle in a few marshmallows and the peppermint baking chips.