Preheat and Prep: Preheat your oven to 350°F (175°C). Line an 8x8 or 9x9-inch square baking pan with parchment paper, leaving an overhang on two sides for easy removal later.

Make the Crust: In a medium-sized bowl, mix together the all-purpose flour, brown sugar, and melted butter until the mixture resembles coarse, wet sand.

Bake the Base: Press the buttery flour mixture firmly and evenly into the bottom of the prepared baking dish. Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden brown.

Add the Caramel: Remove the crust from the oven. While it is still hot, pour the thick caramel sauce evenly over the surface.

Add the Crunch: Sprinkle the chocolate chunks and the chopped nuts (if using) evenly over the warm caramel layer.

Second Bake: Return the pan to the oven and bake for an additional 10 minutes, until the caramel is bubbling and the chocolate chunks are just starting to melt.

Final Topping: Remove from the oven and immediately sprinkle the chocolate chips evenly over the top. Allow them to melt slightly from the residual heat. You can leave them as-is for texture, or gently spread them with an offset spatula. (Sprinkle with flaky sea salt now, if desired).

Cool and Slice: Allow the bars to cool completely in the pan at room temperature. For the cleanest slices, transfer the cooled pan to the refrigerator for at least 1 hour before lifting the bars out using the parchment overhang and slicing into 12 squares.