Chocolate Caramel Shortbread Bars
From Joy Of Baking

Shortbread:
3/4 cup (1 1/2 stick) (170 grams) unsalted butter, room temperature
1/4 cup (50 grams) granulated white sugar
1/2 teaspoon pure vanilla extract
1 1/2 cups (210 grams) all purpose flour
1/8 teaspoon salt
Caramel filling:
1 - 14 ounce (396 grams) can Dulce de Leche or sweetened condensed milk
Chocolate topping:
6 ounces (170 grams) semi-sweet or bittersweet chocolate, cut into pieces
1/2 teaspoon unsalted butter

1. Preheat oven to 350 degrees F (177 degrees C) and place rack in center of oven. Grease with butter (or use a cooking spray) a 9 x 9 inch (23 x 23 cm) pan.
2. For shortbread: in the bowl of your electric mixer, or with a hand mixer, cream the butter and sugar until light and fluffy.
3. Beat in the vanilla extract. Add the flour and salt and beat until the dough just comes together.
4. Press onto the bottom of your greased pan and bake for about 20 minutes, or until pale golden in color.
5. Remove from oven and place on a wire rack to cool while you make the filling.
6. For caramel filling: if using Dulce de Leche then simply warm the caramel in the microwave or in a heatproof bowl set over a saucepan of simmering water.
7. If using sweetened condensed milk, pour the milk into a heatproof bowl and place the bowl over a saucepan of simmering water. Cover and cook, over low heat, stirring occasionally, for 45 to 60 minutes or until the milk has thickened and has turned a light caramel color. (You can also do this step in a microwave oven. Place the sweetened condensed milk in a large microwaveable bowl and cook on medium power for about 4 minutes, stirring halfway through baking time. Reduce the power to medium-low and continue to cook for another 8 to 12 minutes, or until the milk has thicken and has turned a light caramel color. Remove from microwave and beat until smooth.)
8. Remove from heat and beat until smooth.
9. Pour the caramel over the baked shortbread and leave to set.
10. For chocolate topping: melt the chocolate and butter either in the microwave oven or in a heatproof bowl set over a saucepan of simmering water.
11. Pour the melted chocolate evenly over the caramel and leave to set.
12. Cut the shortbread into pieces using a sharp knife.
13. Store the shortbread in the refrigerator to keep the chocolate nice and firm.

Makes 16 - 2 inch (5 cm) squares.