Step 1

For the crust: Preheat the oven to 325 degrees F. Line an 8-by-8 baking pan with parchment that hangs slightly over the edges and set aside.

Step 2

In a medium bowl, mix together the melted butter, granulated sugar and vanilla. Add the flour and kosher salt and stir just until combined, being careful not to overmix.

Step 3

Press the dough firmly and evenly into the prepared baking dish. Bake until the edges are just slightly golden brown, 30 to 35 minutes. Set aside to cool while you prepare the caramel.

Step 4

For the caramel layer: Combine the butter, brown sugar, corn syrup, kosher salt and condensed milk in a medium saucepan. Heat over medium heat, stirring constantly, until the color changes from pale to golden (much like butterscotch). This will take 20 to 25 minutes. Watch closely and reduce the heat as necessary to prevent the bottom from burning.

Step 5

Once a caramel color is achieved, add the vanilla and stir to incorporate. Immediately pour the caramel mixture over the cooled shortbread crust and spread evenly. Set aside to cool while you prepare the chocolate layer.

Step 6

For the chocolate layer: Place the chocolate chips into a medium bowl. In a small saucepan, heat the heavy cream to just simmering. Immediately pour the warm heavy cream over the chocolate chips. Allow to sit for 3 minutes, then gently whisk to form a homogenous mixture. Stir in the corn syrup until incorporated.

Step 7

Pour the ganache over the cooled caramel and spread evenly. Sprinkle flaky sea salt over the top of the bars. Refrigerate until set, about 30 minutes.

Step 8

Cut the bars into even rectangles about 2 inches by 1 inch. This will yield about 32 bars.