Preheat the oven to gas mark 5.
Mix 8oz of the butter and 4oz of the caster sugar in a bowl until soft. Gradually mix in the plain flour, you will need to mix this with your hand towards the end.
Put the mixed dough into a lined swiss roll tray end gently press down until to whole tray is evenlly covered. Place into the preheated oven, for 20-25 mins, until golden. Once cooked, place tray on a cooling rack.
Meanwhile, make the caramel; place 4oz butter, 20z caster sugar, the condensed milk and syrup into a pan. Mix thoroughly and heat gently stirring continuously. Bring to the boil and then gently simmer for 5 mins until the syrup thickens and becomes darker. Leave to cool before pouring it over the shortbread.
Once the caramel has set, gently melt the cooking chocolate and pour over. Refrigerate til set, cut into small slices and enjoy.
Be careful when making the caramel, when it boils it can splash and is very hot.
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