Cook along with Jesse Szewczyk to make these crunchy, perfectly spiced, and understated shortbread cookies that are as delicious dunked into hot coffee as they are eaten all on their own.RecipeMakes 24 bars Shortbread Base1 2/3 cups (214g) all-purpose flour1/3 cup (67g) granulated sugar1/2 teaspoon kosher salt12 tablespoons (1 1/2 sticks/170g) unsalted butter, melted1 large egg yolk1 teaspoon vanilla extractSalted Speculoos Caramel3/4 cup (175 grams) packed light brown sugar4 tablespoons (1/2 stick/57g) unsalted butter1/4 cup (59 ml) light corn syrup1 14-ounce can (414 ml) sweetened condensed milk1/3 cup (90 grams) speculoos cookie butter (see Note)1 teaspoon vanilla extract1 teaspoon kosher saltTopping1/2 cup (about 3 ounces/85 grams) semisweet chocolate chips1/2 cup (about 3 ounces/85 grams) white chocolate chips4 tablespoons (59 ml) whole milk, divided2 tablespoons (36 grams) speculoos cookie butter, dividedFlaky sea salt, for sprinklingMake the shortbread base: Heat the oven 325°F. Grease an 8- by 8-inch baking pan with nonstick pan spray and line with parchment paper, leaving overhang on all four sides. In a large bowl combine the flour, granulated sugar, and salt. Add the melted butter, egg yolk, and vanilla extract and stir together until a soft dough forms. Transfer the dough into the lined baking pan and press into an even layer. Prick the top several times with a fork and bake until the shortbread is slightly puffed and golden brown in the center, 33 to 38 minutes. Remove from the oven and use the bottom of a measuring cup or a metal spatula to press down on the shortbread to compact it slightly. (This will prevent the bars from crumbling when sliced.) Let the shortbread cool for 30 minutes.While the shortbread is cooling, make the caramel: In a medium saucepan fitted with a candy thermometer, combine the brown sugar, butter, corn syrup, sweetened condensed milk, speculoos cookie butter, vanilla, and salt. Cook over medium-low heat, stirring often to prevent burning, until the mixture is smooth, glossy, and registers 240°F on the candy thermometer, about 8 to 11 mins. Pour over the shortbread base, spread into an even layer, and transfer into the fridge. Let cool for 1 hour.As the caramel is cooling, make the topping: Place both the white and semisweet chocolate chips in two separate medium, microwave-safe bowls. Add 2 tablespoons whole milk and 1 tablespoon cookie butter to each bowl. Microwave each bowl on high power in 10 second increments, stirring between each, until the chocolate is completely melted and the mixture is smooth, about 30 seconds total. Transfer the white chocolate ganache into a piping bag or zip-top baggie.Working quickly, pour the dark chocolate ganache over top of the caramel and spread into an even layer. Pipe thin, straight lines of the white chocolate ganache all going the same way. (You might not need all of the ganache.) Use a toothpick to drag it through the lines, alternating the direction you go each time to create a rough chevron pattern. Transfer the bars into the fridge and let set for at least 4 hours, preferably overnight. Sprinkle the top of the bars with flaky sea salt and cut into a 3 by 8 grid to make 24 bars. (For cleaner edges, feel free to trim off the border of the pan before slicing.) Serve chilled or at room temperature.