For the Shortbread:

1. Preheat the oven to 170°c and grease an 8×8″ square pan and line with parchment paper, ensuring the paper overlaps the pan. You’ll be using the overlap to pull the bake from the pan later.
2. In the bowl of an electric mixer, cream the soft butter and brown sugar together on a medium high speed. Add the salt, vanilla and flour, and mix until a soft dough forms. Press the dough into the bottom of your prepared pan making sure to smooth it all evenly.  Prick the dough all over with a fork and chill for 15 minutes.
3. Bake the base for 30 minutes until set and just golden. Remove from the oven and allow to cool completely while you make the caramel filling.

Caramel Filling:

1. Mix the condensed milk, brown sugar, butter and golden syrup in a large, heavy bottomed saucepan and set over a medium heat. Continue to stir or whisk the filling constantly until the caramel registers 105°c on a candy thermometer. You have to be super careful at this stage not to let the bottom of the pan burn, just keep whisking and turn the heat down a smidge if you sense burning.
2. Once your caramel has reached 105°c remove it from the heat and carefully pour it over your cooled shortbread base.  Smooth the topping using a rubber spatular and chill for at least 2 hours.

Chocolate Topping:

1. In a heat proof bowl set over a pan of simmering water, melt the chocolate and oil together, stirring until smooth and melted.
2. Pour the melted chocolate over the chilled caramel filling and tilt the tin to cover evenly.
3. Chill for at least 1 hour, once the chocolate is set remove the shortbread from the pan using the overhanging parchment and cut into squares. Wipe the knife after each cut for a neater square.