Preheat oven to 180°C / 350°F and line a 9" square pan with parchment paper
Put the flour, butter and sugar in a food processer and pulse until the mixture resembles breadcrumbs. If you don't have a food processor you can also rub the butter into the flour and sugar with your fingertips
Squish the mixture together into a dough and press into the base of the square pan
Bake for 30 minutes or until golden
Make the Caramel
Melt the light brown sugar, butter and golden syrup in a pan and bring to the boil
Keep boiling, stirring constantly, until the mixture begins to froth
Remove from the heat and add in the condensed milk and salt
Return to the heat and bring to the boil again
Once boiling, remove from the heat and pour into the square pan, over the baked shortbread base
Allow to cool completely and then transfer to the fridge to set - preferably overnight
Finish
Melt the dark chocolate in 30-second increments in the microwave, stir in the vegetable oil
Pour over the cold caramel shortbread and return to the fridge for an hour before slicing
Remove from the pan and slice. For tips on how to get nice clean slices, read the post above
If you want an extra element, sprinkle the millionaires shortbread squares with a little sea salt before serving