1.Put the biscuits in a food crusher or plastic bag and crush.
2.Melt 100g of butter in a saucepan. Stir in the crushed biscuits. Press the mixture firmly into the bases of the tins. Chill in the fridge for 15 minutes.
3. Put the cooking chocolate in a small heat proof dish and melt. Stir in the remaining butter and cream and mix until a smooth consistency. Spoon in the chocolate mixture into the tart bases and chill in the fridge for 2 hours or until set.
3.When ready to serve decorate with whipped cream and grated chocolate.