Preparation Steps

• Preheat the oven to 350°F. Line a 13x9-inch baking pan with parchment, leaving a 2-inch overhang for easy lifting; lightly grease the parchment.
• Whisk together the flour, cornstarch, baking powder, and salt in a medium bowl and set aside.
• In the bowl of a stand mixer (or using a large bowl and electric beaters), cream the softened butter with the granulated and brown sugars on medium-high speed for 2 to 3 minutes, until pale and fluffy. Beat in the egg yolk and vanilla until incorporated.
• Reduce mixer to low and add the dry ingredients. Mix just until the dough comes together; it will be crumbly but should hold when pressed.
• Press the dough evenly and firmly into the prepared pan to form a compact shortbread base (use the bottom of a measuring cup to get a smooth surface). Bake for 12 to 14 minutes, until the edges are lightly golden and the center is set. Remove from oven.
• While the crust bakes, combine the flaked coconut and ground cinnamon in a bowl. Stir in the jar of caramel sauce until the coconut is evenly coated. Set aside.
• Immediately after taking the crust from the oven, sprinkle 1 1/2 cups of the chocolate chips evenly over the hot shortbread. Let sit 4 to 5 minutes so the chips soften, then spread into a smooth chocolate layer with an offset spatula.
• Spoon the caramel-coated coconut over the melted chocolate and spread into an even layer. Return the pan to the oven and bake 8 to 10 minutes more to set the coconut topping and meld the layers.
• Remove the pan and let cool on a wire rack for about 30 minutes. Melt the remaining chocolate chips in a microwave-safe bowl in 20-second bursts, stirring between each, until smooth. Drizzle or spread the melted chocolate over the coconut layer. Sprinkle with flaky sea salt if using.
• Chill the bars in the refrigerator for about 45 minutes, or until the chocolate and caramel are firm. Use the parchment overhang to lift the block from the pan and cut into 24 bars. Store in an airtight container in the fridge.