Ingredients 
450g plain flour, plus extra for dusting 
300g butter 
150g of caster sugar 

Ingredients for the Caramel 
250g Light soft brown sugar 
300g butter 
4 tbsps golden syrup 
1 tsp vanilla  
2 x 397g tin condensed milk 
Pinch of salt 

Ingredients for the topping 
400g milk chocolate 
100g dark chocolate  
50g white chocolate  

Equipment needed 
20/23cm brownie tin, lined with enough baking parchment to overhanging the edges 

Method
Put all ingredients for the shortbread into a mixing bowl and rub the ingredients together until the mixture looks like breadcrumbs.  You now need to squeeze the mixture together whilst pushing against the side of the bowl to it bring together as a dough, it is a very buttery recipe so will work, just be firm. Tip into the dish and push down, making it as level as you can.   Get a spoon and rub over the top to make it perfectly smooth.  Put into the fridge for 30 minutes and preheat the oven to 170c. 

Once rested, cook in the oven for 20-25 minutes until golden on the top.  Remove from the oven and put to one side.  Whilst you do want it cooked, you don’t want it to be overcooked or the biscuit becomes just too crumbly. 

Put the sugar, butter, golden syrup and vanilla in to a non-stick pan and heat over a medium heat, stirring it all together until everything has melted. Add the condensed milk and bring to the boil, stirring continuously until it begins to boil, this will take 5 minutes or so.  Once boiling, cook for a minute or so until the filling has thickened. Pour the caramel over the base and leave to one side to cool enough to set on top - probably around an hour. 

Put the milk and dark chocolate into a microwaveable bowl and put the white chocolate into a separate bowl. Put the milk chocolate into the microwave and melt on 30 second blasts, stirring fully with a knife between each blasts.  When there are little bits of unmelted chocolate stop, just stir stir stir and it will melt together without getting too hot - this helps it remain shiny. I find this takes between 1 minute 30 seconds and 2 minutes.  Put the white chocolate into the microwave and melt as before, this will most likely only take a minute. 

Pour the milk chocolate over the caramel and slightly tilt to get it even.  Add small spoonfuls of the melted white chocolate over the top of the milk chocolate and then swirl together with a knife for a marbled effect.  Put into the fridge to set.  At a minimum this should be 3 hours although longer is better.  If you cut too soon the slices will not look perfect although the taste will still be wonderful. 

Once set, remove from the tin, take a very large, heavy, sharp knife and run under hot water to heat it.  Dry it then very firmly cut off the very edges of which won’t be perfect. 

Cut into 16-20 equal pieces, you may need to reheat your knife as you go.  I like to make 4 cuts across and 5 down, to get the perfect size.