Preheat the oven to 160°C (325°F) and line a muffin tin with cupcake liners.
Mix the melted butter, Oreo crumbs and black food colouring together and press some of the mixture into each cupcake case. (Reserve a few tablespoons of the crumbs if you want for decorating).
Place in the fridge while you make the cheesecake mixture.
Beat the cream cheese until it is smooth.
Add the egg, vanilla extract, icing sugar. melted chocolate and Greek yoghurt and beat for at least two minutes until the mixture is light and creamy.
Place a dollop of the cheese mixture onto the biscuit base. I start off with a dessert spoon full for each.
Place in the oven for 20 to 25 minutes. The sides should be set and the center will have a very slight wobble.
Allow them to come to room temperature before placing in the fridge to set for at least 4 hours or overnight.
Make the chocolate mousse;
In a bowl place ½ cup (minus two tablespoons) of the cream and whip to soft peaks.
In another bowl melt the chocolate and two tablespoons of cream together and mix through the whipped cream.
Mix through the black food colouring gel until the mousse is black.
Place in the fridge until needed.
Pipe the mousse on top of each cheesecake and decorate each with a sprinkling of Oreo crumbs if you wish.