Pecan Turtle Bars

To prepare crust: Preheat oven to 350 degrees F. Coat a 9-by-13-inch metal baking pan with nonstick cooking spray. Line the bottom with parchment paper, allowing it to slightly overhang opposite edges.

Beat butter, oil and sugar in a mixing bowl with an electric mixer on high speed until creamy and well combined; scrape down the sides. With the mixer on medium, beat in vanilla and salt. With the mixer on low, beat in flour until just combined. (The mixture will be crumbly.) Press the dough evenly into the bottom of the prepared baking pan.

Bake, rotating the pan 180 degrees halfway through, until the shortbread just starts to color around the edges, 18 to 20 minutes. Remove from oven and prick the surface with a fork. (This is important: it helps the chocolate bind to the crust.) Turn off the oven.

Sprinkle chocolate chips evenly over the warm crust. Return the pan to the hot (but turned-off) oven until the chocolate melts, about 3 minutes. Smooth the chocolate with a spatula. Cool on a wire rack until the chocolate is set, refrigerating if desired.

To prepare caramel sauce: Combine 1 cup sugar and water in a small heavy saucepan. Heat over medium-high heat, swirling the pan occasionally, until the sugar dissolves. Continue to cook, without stirring, until the syrup turns a light golden brown, 6 to 10 minutes. Remove from heat and gradually add evaporated milk. (Use caution as you add the milk: the syrup will vigorously bubble in the pan.) Add 1/4 cup butter, vanilla and pinch of salt; whisk until smooth. Set aside until still warm enough to spread, but not hot enough to melt the chocolate layer. (If the caramel becomes too cool to spread easily, reheat it over low, stirring frequently.)

To assemble & top: Spread the caramel over the chocolate. Sprinkle with pecans, gently pressing them into the caramel. Sprinkle with sea salt. Let stand until the caramel is completely set, refrigerating if desired.

To serve, run a knife around the edge of the pan. Using the parchment paper, lift the whole panful out and transfer to a cutting board. Cut into 36 bars.