1. Preheat the oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on two sides, and lightly grease the parchment and sides.

2. In a mixing bowl, beat the softened butter and granulated sugar together until light and creamy.

3. Add the all purpose flour and fine salt to the bowl and mix just until a soft dough forms that holds together when pressed.

4. Press the dough evenly into the prepared pan, making sure to reach all the corners so the layer is level, then prick the surface a few times with a fork.

5. Bake the crust for 18–20 minutes, or until the edges are lightly golden, then remove from the oven and let it cool for 10–15 minutes.

6. While the crust cools, place the soft caramel candies and heavy cream in a medium saucepan over low heat.

7. Stir constantly until the caramels melt completely and the mixture is smooth and thick, then remove from the heat and stir in the vanilla extract.

8. Pour the warm caramel evenly over the cooled shortbread crust, tilting the pan or using an offset spatula to spread it into an even layer.

9. Transfer the pan to the refrigerator and chill for 30–40 minutes, or until the caramel is set and no longer jiggly.

10. In a heatproof bowl, combine the milk chocolate chips and vegetable oil or refined coconut oil.

11. Melt the chocolate mixture in short bursts in the microwave, stirring between each, or over a double boiler on the stovetop until completely smooth and glossy.

12. Pour the melted chocolate over the firm caramel layer and spread it all the way to the edges, tapping the pan gently on the counter to release any air bubbles.

13. If using flaky sea salt, sprinkle it lightly over the top of the chocolate while it is still wet.

14. Chill the bars for 45–60 minutes, or until the chocolate is set but still sliceable.

15. Use the parchment overhang to lift the slab out of the pan and place it on a cutting board.

16. With a sharp knife, cut into bars or squares, wiping the blade clean between cuts for sharp, distinct layers.

17. Serve the bars slightly chilled or at cool room temperature, and store any leftovers in an airtight container.