2-1/2 sticks cold unsalted margarine or butter, cut into cubes
1/4 cup plus 2 tablespoons light brown sugar
1/4 cup plus 2 tablespoons granulated sugar
2-1/2 cups all-purpose flour sifted with 1/2 teaspoon kosher salt
In the bowl of a stand mixer fitted with the paddle, cream the margarine with the sugars at medium speed for 2 minutes. With the mixer at low speed, beat in the sifted flour-and-salt mixture.
Preheat the oven to 350°. Line a 9-by-13-inch baking pan with parchment paper, allowing 2 inches of overhang on the 2 long sides. Transfer the dough to the pan and press it over the bottom and 1 1/4 inches up the side all around. Refrigerate until firm.
Bake the crust for 30 to 35 minutes, until golden brown; halfway through baking, use the back of a spoon to smooth the sides and corners of the crust. Transfer the pan to a wire rack and let the crust cool before filling.
4 tablespoons unsalted margarine
1 cup light corn syrup
1 cup dark brown sugar
5 large eggs
1-1/2 teaspoons pure vanilla extract
1-1/2 teaspoons salt
2 cups pecan halves
Preheat the oven to 350°. In a medium saucepan, melt the unsalted margarine over moderate heat. Remove the saucepan from the heat and whisk in the light corn syrup and dark brown sugar, then whisk in the eggs until thoroughly blended. Whisk in the vanilla extract and salt and stir in the pecans halves until combined.
Pour the pecan filling into the prebaked pie bar crust and bake for about 35 minutes, until the filling is set. Transfer the pan to a rack and let cool completely. Cut into bars and serve.
The pecan pie bars can be refrigerated overnight. Serve chilled or at room temperature.