Preheat oven to 350°F(176°C). Line a 9x13 cake pan with parchment paper (bottom and sides) and lightly spray with pan spray.
For Cake Base: Mix Kinnikinnick White Cake Mix as per directions on box. Add 1 tsp peppermint extract and 3-5 drops of green food colouring. Pour batter into prepared pan and bake for 30 minutes. Remove from oven and let cake cool completely.
For Filling: Whip ½ cup whipping cream and set aside. In a small pot melt chopped chocolate and 1 tbsp 33% cream. Set aside to cool slightly. In a medium bowl, mix cream cheese until soft. Slowly add chocolate mixture and mix until combined. Fold in 1/2 cup whipped cream until combined. Spread filling evenly over prepared cake. Set in fridge for 1 hour.
For Topping: Whip 1 cup whipping cream until soft, add icing sugar and finish whipping. Fold in ½ tsp peppermint extract and 2-3 drops of green food colouring. Spread or pipe evenly over top of cake. Serves 12