Preheat the oven to 350°F (175°C). Line an 8×8-inch or 9×9-inch pan with parchment paper to prevent sticking.

Combine flour and brown sugar in a mixing bowl. Stir in the melted butter until the mixture resembles damp crumbs, then press this mixture firmly into the bottom of the prepared pan to form an even crust.

Bake the crust for 10-12 minutes until the edges are lightly golden brown.

Pour the thick caramel sauce over the warm crust, spreading it evenly with a spatula.

Scatter the semi-sweet or dark chocolate chunks and chopped nuts over the caramel.

Bake again for about 10 minutes until the caramel is bubbling and the chocolate has softened nicely.

Sprinkle chocolate chips immediately over the top, allowing the residual warmth to gently melt them.

Optional: Add a pinch of flaky sea salt before cooling.

Cool completely in the pan, then chill for 1 hour to set. Once set, slice into 12 bars for serving.