Preheat the oven to 180°C/fan 160°C/gas 4 and line a baking tin 18cm x 28cm with non-stick baking parchment.
To make the shortbread, cream together the sugar and butter until pale and fluffy then add the flour and mix to form a soft dough.
Tip into the baking tin and with your fingertips, spread out to cover the base of the tin in an even layer. Bake in the oven for 15 minutes until golden, then remove and set aside to cool.
Next make the caramel. Add all the ingredients to a medium saucepan and heat gently until the butter has melted and the sugar dissolved, stirring occasionally.
Increase the heat and bring the caramel to the boil and bubble for 5-10 minutes until the sauce thickens and turns a golden caramel colour. Pour onto the shortbread and smooth to cover in an even layer, leave in the fridge for a couple of hours until set.
For the chocolate topping, break the dark and milk chocolates into small pieces and melt in a bowl in the microwave or over a pan of gently simmering water.
Melt until completely smooth and pour over the caramel layer, tapping the tin on the work surface so that it settles in an even layer.
Top with chopped creme egg pieces and then with the tip of a knife swirl the pieces into the chocolate slightly. Leave to cool completely before cutting into squares with a sharp knife.
The Cadbury Creme Egg cook book will be available nationwide at £9.99 in Waterstones, Asda, Tesco and Sainsburys, as well as online at Cadbury Gifts Direct.
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