2 cups all-purpose flour
1/2 cup sugar
pinch of table salt
2 1/2 sticks cold unsalted butter, cut into pieces
1 (14-ounce) can sweetened condensed milk
1 tablespoon instant espresso or coffee granules
3 tablespoons light corn syrup
1 1/2 cups high-quality bittersweet chocolate chips
3 tablespoons white chocolate chips
Prepare a 9 × 13-inch baking pan by greasing it with cooking spray and then lining the bottom with parchment paper.
To make the crust, combine the flour, sugar (1/4 cup), and salt in the bowl of an electric mixer fitted with the paddle attachment.
With the machine running on low speed, gradually add the pieces of butter (12 tablespoons). Raise the speed to medium-low and mix for 3 minutes, until of the butter has been incorporated.
Turn the dough out into the prepared pan, and evenly press it over the bottom. Prick the dough all over with the tines of a fork. Refrigerate the dough for 20 minutes.
Preheat the oven to 350°F.
Bake, rotating the pan halfway through, for 11 minutes, until it is golden around the edges. Let cool.
To make the caramel, combine the sweetened condensed milk, sugar (1/4 cup), coffee granules, butter (8 tablespoons), and corn syrup in a medium heavy-bottomed saucepan set over low heat.
Stir constantly until butter begins to melt. Increase temperature to medium-low, and continue to stir until the mixture begins to boil.
Cook for 8 to 10 minutes, until the caramel is thick enough that when you drag the spoon through the middle, the indentation remains for 2 seconds. Be very careful at this point because the caramel is very hot.
Pour the caramel over the crust and spread it out in an even layer, working quickly, as the caramel will firm up as it cools. Let the caramel cool completely.
Loosen the edges of the crust with a metal spatula. Invert the pan over a large baking sheet, releasing the bars onto the baking sheet. Remove the parchment, and invert the bars again onto a cutting board.
To make the chocolate layer, put the bittersweet chocolate in a micro- wave safe bowl. Heat it on high power in 1-minute intervals, stirring between heatings to prevent the chocolate from burning, until it has melted.
Spread the chocolate evenly over the caramel.
n a second microwave-safe bowl, melt the white chocolate in the same way. Using a pastry bag (or a plastic sandwich bag with a small hole cut into one corner), pipe stripes of white chocolate over the dark chocolate.
Let the chocolate layer cool for 20 minutes. When the chocolate is almost set but not quite hard, use a small, thin paring knife to cut 2-inch squares. The caramel can be messy, so be sure to clean the knife after each cut.
Note: After cutting these into squares, you’ll be left with the not-so-attractive edges. We cut them into bits, freeze them, and then toss them on top of ice cream.