Place the oven rack on the lowest level in the oven. Preheat the oven to 150C/Fan130C/Gas Mark 2. Grease and base line a 20cm deep sided non-stick loose base round cake tin with baking parchment and grease again. Place the biscuits in a large bag and bash with a rolling pin until they resemble fine crumbs or whizz the biscuits into crumbs in a food processor. Melt the butter in a saucepan and mix in the biscuit crumbs. Place the crumbs in the cake tin and press down with a spoon to form an even layer. Place in the freezer.
Melt the chocolate in a large mixing bowl set over a saucepan of simmering water, do not allow the water to touch the base of the saucepan. Remove from the saucepan and set aside to cool.
Meanwhile, mix the cream cheese and sugar together in a large mixing bowl. Crack the eggs in one at a time and stir to combine. Add 1 tablespoon of the cheese mixture to the chocolate and stir to combine. Repeat the process until all the cheesecake mixture has been added to the chocolate.
Pour the chocolate mixture into the cake tin and spread to form an even top. Place on a baking tray and bake for 55 minutes. Turn the oven off and leave the door ajar with a wooden spoon until the oven is cold. Cover and place in the fridge for 6 hours or preferably over night.
To decorate, remove the cheesecake from the cake tin and place on a serving plate. Melt the chocolate in a mixing bowl set over a saucepan of simmering water, do not allow the water to touch the base of the saucepan. Remove from the heat. Fill a piping bag with the chocolate and pipe lines over the cheesecake. Alternatively, use a teaspoon to drizzle the chocolate over the cheesecake. Allow to set in the fridge. Remove from the fridge 30 minutes before serving. Serve with Greek yogurt.