Preheat oven to 350 degrees. Spray a 9x9 square baking pan with non-stick spray and line with parchment paper, leaving an overhang to use as a sling to pull the bars out of the pan.

Add 1 cup unsalted butter, the powdered sugar, and 1/2 teaspoon fine sea salt to the bowl of a stand mixer fitted with the paddle attachment. Beat until the butter is smooth and creamy, scraping down the bowl as needed.

Bake the crust for about 20 minutes, or until the edges start to turn golden.

While the crust bakes, prepare the caramel. Add the sweetened condensed milk, 1/2 cup (8 tablespoons) cubed butter, corn syrup, 1/2 teaspoon fine sea salt, vanilla extract, and light brown sugar to a medium saucepan. Heat over medium heat and whisk constantly.

Cook the caramel, still whisking constantly, until it reaches 225 degrees F. As soon as it reaches 225F, pour directly onto the baked shortbread crust. Cool the caramel to room temperature before making the ganache.

To make the ganache, add the chocolate chips, heavy cream, and 2 tablespoons butter to a medium microwave-safe bowl. Heat in the microwave at 50% power for 1 minute. Stir well to combine. Continue to heat at 50% power for 20 second intervals, stirring after each time, until the chocolate is completely melted.

Pour the ganache over the cooled caramel layer and refrigerate for at least 1 hour before slicing and serving.