Melt the butter in a small saucepan, then stir in the crushed biscuits. Divide between 2 x 8cm loose-bottomed round tart tins and using a teaspoon, press the mixture over the base and up the sides of the tins. Chill in the fridge.
Carefully cut the Creme Eggs in half down the seam and pull apart, then using a teaspoon, scoop out the 'goo' from the centre and place in a small saucepan (or place the 'goo' in a microwaveable bowl and microwave on high power for 10-20 secs depending on microwave rating.)
Break the chocolate shells into pieces, then place in a small bowl with the cream. Place the bowl over a pan of simmering water and stir until you have a smooth chocolate mixture. Allow to cool slightly, then pour into the tart cases. Chill for 2-3 hrs until set.
Just before serving remove the tarts form the tins. Place the 'goo' in the saucepan and heat gently until melted together, do not stir, but shake the pan from time to time. Pour over the tarts and serve immediately decorated with a little grated chocolate.