Preheat your oven to 150C

In a bowl, cream together the sugar and butter.

Add in the flour and mix until a crumbly dough is formed.

Press the dough into the bottom of your tin, pierce with a fork all over and bake for 20 minutes until just set.

Whilst the shortbread is cooking, start making your caramel.

Add all caramel ingredients to a big, heavy bottomed pan (the mixture will bubble up quite substantially as it cooks!) and bring to the boil, stirring consistantly. Use a sugar thermometer (or a food probe) to bring the temperature to 116°C (it may say soft boil on your thermometer) Take off the heat and stir occasionally, as the sugar sets the caramel will thicken.

Pour the caramel over the cooled shortbread and leave to set in the fridge.

Pour the melted chocolate over the set caramel and stick in the fridge to set.

Once every element is set, take out of the fridge to warm up slightly before use a sharp, warmed chefs knife to cut into pieces.