Prepare the Crust:

1. Adjust oven rack to middle position and preheat the oven to 350 degrees F. Line a 9x9-inch pan with aluminum foil, leaving extra foil hanging over the edges of the pan. (Using 2 long sheets overlapped perpendicularly works well.) Press and smooth foil into the corners of the pan. Grease the foil and set pan aside.
2. Pulse the flour, baking powder, salt, brown sugar, and pecans in food processor until the mixture resembles coarse corneal. Add butter and pulse until mixture resembles breadcrumbs. Press mixture evenly into the prepared pan and bake until crust is lightly golden brown and springs back when pressed, about 20 minutes.

For the Filling:

1. While the crust is baking, whisk together the melted butter, brown sugar, corn syrup, vanilla, bourbon, and salt in medium bowl until just combined. Add egg and whisk until incorporated.
2. Pour filling mixture over hot crust and sprinkle pecans evenly over the top. Bake until top is golden brown and surface begins to crack, 22 to 25 minutes. Let cool on wire rack for 1 hour. Remove bars from pan by lifting the foil from the pan and moving entire contents of pan to a cutting board. Cur into desired sized bars and serve.