Shortbread Layer

In the bowl of a stand mixer, fitted with a paddle attachment, combine the butter, sugar, and shortening until light and fluffy. Beat on high for 1 minute or until light and fluffy. Scrape down the sides of the bowl using a rubber spatula.

Add the egg yolks and mix until just combined. Add vanilla and salt and mix to combine. Add flour and mix on medium speed for 1 minute until a smooth dough forms.

Remove the dough from the mixing bowl and mold it into a 1" thick disc.  Cover with plastic wrap and place in the fridge to chill for 1 hour.  

Preheat the oven to 350°F. Line a 9x9 pan with parchment paper and lightly spray with baking spray.

Once the dough has been chilled, remove from the fridge and evenly spread into the prepared baking dish. Place into the preheated oven on the middle rack and bake for 30 minutes.

Once baked, remove from the oven and place on a wire cooling rack.  While the shortbread is cooling, make the caramel.

Caramel Layer

In a medium-sized saucepan, add the sweetened condensed milk, brown sugar, butter, and corn syrup. Cook over medium heat, stirring occasionally until the ingredients are melted and well combined.

Turn the heat down to low and simmer for 10-15 minutes or until the color changes to a rich caramel.

Remove from the heat and whisk in the vanilla and salt.

Pour the caramel onto the baked shortbread. Set aside to cool completely.  While the caramel is cooling, make the chocolate layer.

Chocolate Layer

Add chocolate chips to a medium-sized bowl. Set aside.

In a separate microwave-safe bowl add the heavy cream and microwave for 1 minute.

Once the heavy cream is heated, pour it over the chocolate chips and let sit for 1 minute. Then briskly whisk the chocolate minute until it becomes very smooth in texture.  

Pour the chocolate mixture over the cooled caramel. Cover the baking dish with plastic wrap and place it in the refrigerator.

Cool for at least 1-2 hours before serving. Once cooled, cut into 9 pieces and serve.