For crust: Preheat the oven to 350°F. Butter or spray the bottom and sides a 13-by-9-inch baking pan with baking spray. Line the pan with parchment paper or foil letting the excess extend over the edges of the pan.
Cube the butter and place in a saucepan over medium heat. Cook until the butter smells nutty and the solids have turned brown, 6 to 8 minutes. Immediately pour the butter into a medium bowl to stop the cooking. Whisk in the sugar and salt. Add the flour, and stir until it is fully moistened. Press the crust evenly into the bottom of the prepared pan. (The crust will be moist. Press carefully to reach all edges and corners of the pan).
Bake for 15 minutes. Remove and lightly press down any large bubbles in the crust.
For the filling: In a large bowl, whisk together the melted butter, corn syrup, brown sugar, eggs, vanilla, and salt until smooth. Stir in the pecans. Pour over the baked crust.
Bake at 350°F until the topping is puffed and set (it should not wiggle), 30 to 35 minutes. Let cool completely in the pan. Use the excess parchment or foil to lift the bars out of the pan. Cut into squares to serve.
