Make the shortbread base:
Preheat your oven to 350°F (175°C). Line a 9×9-inch baking dish with parchment paper. In a large bowl, cream together the butter and sugar until light and fluffy. Add flour and salt, and mix until a crumbly dough forms. Press the dough evenly into the prepared pan. Bake for 20-25 minutes or until lightly golden. Let it cool completely.

Make the caramel layer:
In a saucepan over medium heat, melt the butter. Stir in brown sugar, corn syrup, and sweetened condensed milk. Bring to a gentle boil, stirring constantly, and simmer for 5-7 minutes until thickened and golden. Pour the caramel over the cooled shortbread and spread it evenly. Chill in the fridge for 1 hour or until set.

Make the chocolate topping:
Melt the chocolate chips and butter together in the microwave or over a double boiler, stirring until smooth. Pour over the caramel layer and spread evenly. Chill again until the chocolate is firm, about 30 minutes.

Serve:
Once everything is set, remove from the pan and cut into squares. Serve chilled or at room temp.