Preheat oven to 350 degrees. Line the bottom and sides of a 13x9-inch pan with aluminum foil, allowing a couple of inches to extend over the sides. Lightly grease foil.
Bake pecans in a single layer in a shallow pan for 8 to 10 minutes or until lightly toasted and fragrant, stirring halfway through.
In a food processor, pulse flour, powdered sugar and 3/4 cup butter until the mixture resembles coarse meal. Press the mixture into the bottom and 3/4 inch up the sides of the previously prepared pan.
Bake crust for 20 minutes or until edges are lightly browned. Cool completely, about 15 minutes.
Bring brown sugar and remaining 3 ingredients to a boil in a saucepan over medium-high heat. Stir in toasted pecans, and spoon hot filling into prepared crust.
Bake for 25 to 30 minutes or until golden and bubbly. Cool completely on a wire rack. Using foil sides as handles, lift baked and cooled bars from the pan; transfer to a cutting board and cut into bars.