1. Line an 8 by 8 inch baking pan with parchment paper, leaving an overhang on two sides, lightly grease the parchment, and preheat the oven to 350 degrees F.

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

3. Add the flour and salt to the bowl and stir just until the dough comes together with no dry spots remaining.

4. Press the shortbread dough evenly into the prepared pan, smoothing the top with the back of a measuring cup.

5. Bake the shortbread for 18 to 20 minutes, until the edges are lightly golden and the surface looks set, then let it cool for 10 to 15 minutes.

6. While the base cools, add the unwrapped caramel candies, heavy cream, and 2 tablespoons unsalted butter to a saucepan over low heat.

7. Stir constantly until the caramels are fully melted and the mixture is smooth and glossy.

8. Pour the warm caramel over the shortbread base, tilting the pan so it covers the surface evenly, then refrigerate for 30 to 45 minutes until set but still slightly soft.

9. Place the milk chocolate and coconut oil in a microwave safe bowl and heat in 20 to 30 second bursts, stirring after each, until melted and smooth.

10. Pour the melted chocolate over the chilled caramel layer and spread it into an even layer, sprinkling flaky sea salt on top if using.

11. Refrigerate the pan again for 30 to 45 minutes, until the chocolate is set but not rock hard.

12. Use the parchment overhang to lift the slab out of the pan onto a cutting board, warm a sharp knife under hot water, dry it, and slice into bars, wiping and reheating the knife between cuts for clean layers.