Shortbread
2 cups all-purpose flour
2 teaspoons baking powder
1/4 teaspoon salt
1 cup (2 sticks) unsalted butter, at room temperature
1/2 cup sugar
Caramel
1/2 cup (1 stick) unsalted butter, cut into 8 pieces
1/2 cup sugar
2 tablespoons light corn syrup
1 14-oz can sweetened condensed milk
Chocolate
8 oz chocolate, finely chopped (I used bittersweet)
1 teaspoon light corn syrup
1/2 cup (1 stick) unsalted butter, cut into 8 pieces
Fleur de sel for sprinkling (optional)
Directions:
Preheat oven to 325 F. Line a 9x13-inch baking pan with parchment paper.
To make the shortbread layer: Whisk the flour, baking powder and salt together in a medium bowl. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium speed until well combined, about 2 minutes. With the mixer on low, gradually add the dry ingredients and beat just until combined. Transfer the dough to the prepared pan and press into an even layer over the bottom (it'll be a fairly thin layer). Bake for 15-18 minutes, or until the crust is golden brown. Transfer the pan to a wire rack and cool completely.
To make the caramel layer: Combine the butter, sugar, corn syrup and sweetened condensed milk in a medium saucepan. Set the pan over medium heat. Stir occasionally until the butter is melted. Increase the heat to medium-high, and bring the mixture to a boil. Reduce the heat to medium-low and simmer, whisking constantly, until the mixture thickens and turns a light caramel color. This may take 10 minutes or more, so be patient. Pour the caramel mixture over the cooled shortbread and spread in an even layer. Allow to cool completely, then chill briefly (I stuck mine in the fridge overnight, but you just want to chill enough that it won't melt when you add the warm chocolate in the next step).
To make the chocolate layer: Add the chocolate, corn syrup, and butter to a heatproof bowl and set over a pan of simmering water. Heat, stirring occasionally, until everything is melted and the mixture is smooth and glossy. Pour the chocolate over the chilled caramel and spread into an even layer with an offset spatula. Let cool for a few minutes, then sprinkle the top with the fleur de sel (if using). Let the chocolate set completely before slicing and serving.
