Heat the oven to 350°F. Brush or spray the bottom of the pan lightly with oil. Line a 13 x 9 x 2-inch baking pan with parchment paper, leaving an inch or so overhang on two side to lift the bars from the pan after baking.
In the bowl of a food processor, pulse the flour, confectioners’ sugar, and salt. Add the butter all at once, then pulse until the mixture resembles coarse breadcrumbs. Add the egg and pulse until the dough comes together in a ball.
2 cups unbleached, all-purpose flour, 1/2 cup confectioners' sugar, 1/4 teaspoon fine sea salt, 12 tablespoons unsalted butter, 1 large egg
Roughly divide the dough evenly over the pan and press it evenly into the pan and up the sides by about 1 inch. Bake until pale golden, 20 minutes.
Meanwhile, make the filling. Coarsely chop the toasted pecans. In a medium saucepan over medium high heat, melt the butter until it foams, then browns. Remove the pan from the heat and stir in the brown sugar, granulated sugar, salt, vanilla extract, and orange blossom water. Add the pecans and stir to combine, then add the egg and stir to combine.
1 cup unsalted butter, 3/4 cup dark brown sugar, 1/2 cup granulated sugar, 1/2 teaspoon fine sea salt, 1 tablespoon vanilla extract, 1 teaspoon orange blossom water, 3 cups pecan halves or pieces, 1 large egg
When the crust is done baking, remove it from the oven and pour the pecan mixture over the warm crust.
Bake until the center is set, 20-25 minutes.
Cool to room temperature. Run a knife around the perimeter of the pan interior, lift the block out, and transfer to a cutting board. Cut into 2-inch squares.