**Prepare the Shortbread Crust**

Preheat oven to 350°F (175°C). Line a 9x13-inch baking dish with parchment paper.

In a mixing bowl, cream together the butter and sugar until light and fluffy. Add the flour and salt, mixing until a crumbly dough forms.

Press the dough evenly into the bottom of the prepared baking dish. Bake for 18-20 minutes or until lightly golden. Let 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. Reduce heat and simmer for 5-7 minutes until thickened and golden brown. Remove from heat and stir in vanilla extract.

Pour the caramel over the cooled shortbread crust and spread evenly. Let set at room temperature for 30 minutes or refrigerate for faster cooling.

**Prepare the Chocolate Topping**

In a microwave-safe bowl, melt the chocolate chips with vegetable oil in 30-second intervals, stirring in between until smooth.

Pour the melted chocolate over the caramel layer and spread evenly. Let the chocolate set at room temperature or in the refrigerator for at least 1 hour.

**Slice and Serve**

Once fully set, lift the bars from the pan using parchment paper. Cut into squares or bars and serve.