Preheat the oven to 350°F with a rack in the center position. Line the bottom and sides of a 9- by 13- by 2-inch pan with an aluminum foil, extending about 2 inches over the sides (creating a foil “sling.”)

GROWN UP ALERT:

Combine the flour, confectioners’ sugar, and salt in the bowl of a food processor. Pulse to combine. Add the butter and pulse until the dough just comes together, about 1 to 2 minutes.

Spread the dough into the prepared pan and press firmly to smooth the top. Using a fork, prick the surface of the dough, making marks spaced about 1 inch apart.

GROWN UP ALERT:

Bake the shortbread until it is golden brown and firm to the touch, about 35 minutes. Set aside to cool completely in the pan.

Spread the dulce de leche over the dough, forming an even layer using a small offset spatula. Refrigerate until slightly firm, about 1 hour.

GROWN UP ALERT:

Place the chocolate in a microwave-safe bowl and into the microwave for 30 seconds. Carefully remove and stir with a rubber spatula. Repeat this process until the chocolate is melted and smooth. Spread the chocolate over the dulce de leche. Sprinkle with sea salt.

Let stand at room temperature until the chocolate sets, about 10 minutes. Using the sides of the aluminum foil as a sling, carefully remove the layered cookie from the pan. Peel back the aluminum foil and transfer to a cutting board.

GROWN UP ALERT:

Using a serrated knife, cut in half crosswise, then cut both pieces in half lengthwise, forming 4 quarters, each about 9- by 3-inches. Cut each quarter crosswise into 8 bars, about 1- by 3-inches in size. Store at cool room temperature for up to 2 hours or refrigerate for up to 1 week.