01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper.
02 - Combine flour, sugar, salt, and softened butter in a bowl until mixture becomes crumbly. Press dough firmly and evenly into the prepared pan. Bake for 15-18 minutes until edges turn lightly golden. Allow base to cool completely.
03 - Heat sugar in a saucepan over medium heat, stirring constantly until sugar melts and turns amber-colored. Add cubed butter and stir until completely melted. Slowly pour in heavy cream while stirring continuously—mixture will bubble vigorously. Cook until smooth, then remove from heat and stir in vanilla extract and salt. Let cool for 5 minutes.
04 - Distribute chopped nuts evenly across the cooled shortbread base. Pour warm caramel over the nuts, spreading smoothly to cover the entire surface. Refrigerate for 30 minutes until caramel layer sets.
05 - Melt chocolate and 2 tablespoons butter together using a heatproof bowl set over simmering water or in the microwave using 30-second intervals. Stir continuously until completely smooth and glossy.
06 - Pour melted chocolate mixture over the chilled caramel layer, spreading evenly with an offset spatula. Refrigerate for at least 1 hour until chocolate is completely firm and set.
07 - Lift the chilled block from the pan using parchment paper edges. Transfer to a cutting board and slice into 16 equal bars using a sharp knife, wiping the blade clean between cuts for clean edges.