Preheat the oven 350°F. Grease a 13 x 9 x 2″ baking tin with butter.
In a bowl, use your fingertips to rub together the butter and flour for the shortbread base, then mix in the sugar. Press the mixture into the baking tin and bake in the oven for 20 minutes or until lightly golden. Leave the oven turned on.
While the base is cooking, prepare the salted caramel. Place all the topping ingredients, except the chocolate, in a saucepan over a low– medium heat and allow to melt, then bring to the boil and simmer for 10–15 minutes until you have achieved a nice toffee color, stirring regularly to ensure the sauce doesn’t catch on the bottom of the pan.
Pour the caramel over the shortbread base and place back in the oven to cook for 10 minutes. When done, remove the baking tin from the oven and allow to cool completely.
Melt the chocolate in a heatproof bowl set over a pan of shallow simmering water, then pour the melted chocolate over the cooled caramel and spread evenly with a palette knife. Once the chocolate has set, slice into 16 squares, or smaller ones if you want them to stretch further.