Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving overhang on the long sides for easy lifting. Lightly grease the parchment.

Make the shortbread base: In a mixing bowl, combine the flour, granulated sugar, 1/2 tsp salt, and 1 cup softened butter. Beat or stir until the mixture forms a soft, even dough. Mix in 1 tsp vanilla extract.

Press the dough evenly into the prepared pan, smoothing the top and pushing it slightly up to the edges and corners so the layer is level.

Bake the crust for 18–20 minutes, until the edges are lightly golden and the top looks set and dry. Place the pan on a wire rack to cool slightly while you prepare the topping.

Toast the coconut: Spread the shredded coconut on a large baking sheet in an even layer. Bake at 350°F for 6–8 minutes, stirring once or twice, until lightly golden and fragrant. Watch closely so it does not burn. Let cool slightly.

Make the caramel coconut layer: In a medium saucepan over low to medium-low heat, combine the unwrapped caramels and heavy cream. Stir constantly until the caramels are fully melted and the mixture is smooth.

Remove the caramel from the heat and stir in the toasted coconut, 1/4 tsp salt, and 1 tsp vanilla extract. The mixture should be thick but spreadable, similar to warm peanut butter.

Assemble the bars: While the crust is still just warm (not hot), dollop the caramel coconut mixture over the shortbread. Use a greased spatula or the back of a spoon to gently spread it into an even layer, pressing lightly so it adheres to the crust. Let cool to room temperature, about 20–30 minutes.

Melt the chocolate: Place the semisweet chocolate chips and milk chocolate chips (if using) in a heatproof bowl. Microwave in 20–30 second bursts, stirring after each, until just melted and smooth. Alternatively, melt over a double boiler on the stove.

Spread the chocolate over the cooled caramel coconut layer, reserving 2–3 tablespoons if you want a decorative drizzle. Smooth into a thin, even layer that fully covers the surface.

If drizzling, rewarm the reserved chocolate briefly if needed, transfer it to a small piping bag or a zip-top bag with a tiny corner snipped off, and drizzle over the top in thin lines.

Chill the pan in the refrigerator for 45–60 minutes, or until the chocolate is firm and the bars are well set.

Use the parchment overhang to lift the slab from the pan onto a cutting board. Let sit at room temperature for 5–10 minutes to soften slightly, then use a sharp knife to cut into 24 bars or smaller bite-size squares. Wipe the knife between cuts for clean edges.