Line a 9×9 inch square pan with two pieces of parchment paper, creating a sling for easy removal.

In a medium bowl, cream the butter until smooth, then add the powdered sugar and vanilla and beat for 2 more minutes.

With a rubber spatula, fold in the flour and salt until just combined.

Press the dough into the prepared pan and use the back of a spoon or small measuring cup to pack it in and level it out.

Place in the fridge to chill for 30 minutes.

While the base is chilling, preheat the oven to 325 degrees F.

Bake the shortbread for 30-35 minutes or until it is an even light golden brown.

Allow to cool completely before pouring the caramel on top. 

In a medium bowl, heat the heavy cream and butter until the butter has completely melted. Set aside.

In a large, deep saucepan combine the sugar and light corn syrup. Heat over low-medium heat, stirring until the sugar has dissolved.*

Increase the heat to medium-high, and stir frequently. After about 10 minutes, it will turn amber in color.

Remove the pan from the heat and stir in the heavy cream and butter mixture. It will bubble and rise rapidly. 

Return the pan back to the medium-high heat. Stir frequently until it reaches 248 degrees F. 

Once it comes to temperature, remove from heat and stir in the tahini and vanilla. 

Immediately pour over the cooled shortbread crust.

Allow the caramel to cool down a little before placing in the fridge overnight. You could also leave it at room temperature for several hours to set. 

In a medium bowl, heat the chocolate and oil until fully melted and smooth. 

Pour over the set tahini caramel and spread into an even layer. 

Place in the fridge until solid. 

Cut the millionaire's shortbread into 16 bars (or more), sprinkle with flaky sea salt, and enjoy!