Chocolate Dulce de Leche Bars

Fudgy cookies go Latin with an infusion of dulce de leche, a sweet milk caramel similar to cajeta and arequipe. These cool treats are happily portable on their crisp shortbread crusts.

Makes 24 bars

For shortbread crust:
1 stick unsalted butter, softened
1/3 cup packed light brown sugar
1/2 teaspoon pure vanilla extract
1/2 teaspoon salt
1 cup all-purpose flour

For chocolate dulce de leche:
1 cup heavy cream
1 cup dulce de leche
4 large egg yolks
5 ounces 60%-cacao bittersweet chocolate, finely chopped (preferably in a food processor)

Make shortbread crust:

Preheat oven to 375°F with rack in middle.

Butter a shallow 9- to 9 1/2-inch square baking pan (1 to 1 1/2 inches
deep). Line bottom and 2 sides with parchment paper, leaving an overhang.
Butter parchment.

Blend together butter, brown sugar, vanilla, and salt in a bowl with a fork.

Sift in flour and blend with fork until a soft dough forms.
Make chocolate dulce de leche: Bring cream and dulce de leche to a
simmer in a small heavy saucepan, stirring with a wooden spoon until dulce
de leche has dissolved.

Whisk together yolks in a bowl, then slowly whisk in hot cream mixture.

Return to pan and cook over medium heat, stirring constantly, until pan is
visible in tracks of spoon and mixture registers 170°F on an instant-read
thermometer. Remove from heat and whisk in chocolate until melted.

Make bars: Pour chocolate mixture over cooled shortbread and chill,
uncovered, until cold and set, about 2 hours.

Run a small knife around edges to loosen, then transfer to a cutting board
using parchment.

Cut with a hot clean knife (dip in hot water and wipe clean between cuts)
into 24 bars. Chill until ready to serve.

Chocolate dulce de leche bars can be chilled in an airtight container up
to 1 day.