Thought I'd give this a try seeing as I always have the urge to buy it when I see it in the shops! A lot of Caramel so I recommend cutting it into smaller squares...
Sorry no pictures for the how-to steps, it's quite straight forward though :-)
Preheat the oven to 180Celsius/350Fahrenheit/Gas Mark 4. Put the 115g butter, flour and 55g caster sugar in a food processor and process (I don't have a food processor so I just used an electric whisk and my hands) until they bind together. Then put into a 9-inch tin (I used a bigger one and it still worked fine), then pop into the oven for 20-25 minutes or until golden.
For the filling, put the remaining 200g of butter, remaining 115g caster sugar, golden syrup and condensed milk into a saucepan and heat until the sugar has dissolved. When that has happened bring to the boil then simmer for 6-8 minutes (it should thicken a bit), remember to stir constantly.
When the shortbread base is done remove from the oven and pour over the caramel filling and pop into the fridge to chill.
The chocolate topping is basically just melted chocolate. You can do this in the microwave or on the hob. Once melted leave to cool slightly then pour over the caramel and spread evenly. Leave this to chill in the fridge until set then cut into pieces and enjoy!!