1. Make the Shortbread Cookie Layer:

• Preheat and Prep: Preheat oven to 350°F (175°C). Grease an 8×8-inch square baking pan. Line the pan with parchment paper, leaving an overhang on two sides for easy removal. Lightly grease the parchment paper.
• Cream Butter and Sugar: In a large bowl, using an electric mixer (hand mixer or stand mixer with paddle attachment), cream together the room temperature butter, granulated sugar, and vanilla extract until light and fluffy, about 3 minutes.
• Add Flour: Gradually add the all-purpose flour, mixing on low speed until just combined. The dough will be crumbly.
• Press into Pan: Press the dough firmly and evenly into the bottom of the prepared baking pan.
• Dock the Dough: Use a fork to poke holes all over the surface of the dough. This prevents it from puffing up unevenly while baking.
• Bake: Bake for 25 minutes, or until the edges are just beginning to turn golden brown.
• Cool Crust: Carefully lift the parchment paper and the baked crust out of the pan and place it on a wire rack to cool completely while you make the caramel layer.

2. Make the Caramel Layer:

• Combine Ingredients: In a medium, heavy-bottomed saucepan, combine the sweetened condensed milk, salted butter, brown sugar, light corn syrup, and salt.
• Cook Caramel: Place the saucepan over medium heat. Cook, whisking constantly, until the mixture comes to a slow boil.
• Simmer and Thicken: Reduce the heat to maintain a steady simmer. Continue cooking, whisking constantly, for about 20 minutes, or until the caramel has visibly thickened, darkened to a rich caramel color, and coats the back of a spoon. If using a candy thermometer, the temperature should reach 220-225°F (104-107°C). Patience is key here; continuous whisking prevents scorching.
• Add Vanilla: Remove the pan from the heat and immediately stir in the vanilla extract.

3. Assemble Crust and Caramel:

• Place the cooled shortbread crust (still on the parchment paper) back into the baking pan.
• Carefully pour the hot caramel evenly over the cooled cookie crust.
• Let the caramel cool on the counter for about 10 minutes, then transfer the pan to the refrigerator and chill for at least 1 hour, or until the caramel is firm.

4. Make the Chocolate Layer:

• Heat Cream: Place the chocolate chips in a medium-sized microwave-safe bowl. Heat the heavy cream in a small saucepan over medium heat or in the microwave until it is very hot and steaming, but not boiling.
• Melt Chocolate: Pour the hot cream over the chocolate chips. Cover the bowl with a plate and let it sit undisturbed for 5 minutes.
• Whisk Smooth: Whisk the mixture gently until the chocolate is completely melted and the ganache is smooth. If unmelted chocolate remains, microwave in 15-second intervals, stirring after each, until smooth.
• Add Vanilla: Stir in the vanilla extract.
• Cool Slightly: Let the chocolate ganache cool for a few minutes.

5. Finish the Bars:

• Pour Chocolate: Pour the slightly cooled chocolate ganache over the chilled, firm caramel layer. Use an offset spatula to spread it into an even layer if needed.
• Add Salt: Let the chocolate layer cool on the counter for 5-10 minutes, then sprinkle evenly with the finishing salt. Waiting prevents the salt from dissolving.
• Final Chill: Let the bars cool completely on the counter for about 1 hour. Then, cover the pan tightly with plastic wrap and refrigerate for a minimum of 5 hours, or preferably overnight, to allow all layers to set firmly.

6. Slice and Serve:

• When ready to serve, use the parchment paper overhang to lift the entire block of bars out of the pan. Gently peel away the parchment paper from the sides.
• Use a long, sharp knife to slice the bars into squares or rectangles. For perfectly clean cuts, run the knife under hot water and wipe it clean after each slice.