Preheat the oven to 350 degrees.
Line an 8-inch square baking pan with parchment paper. Leave an overhang so that you can remove the lemon bars once cooled.
Combine flour, sugar, and salt in the bowl of a stand mixer.
Add butter and beat until incorporated. (Alternatively, you can use a food processor.)
Stir in the toasted, chopped pecans.
Press the shortbread mixture into the bottom of the 8-inch pan, and bake for 20 minutes or until lightly browned.
While the crust is baking, whisk together the granulated sugar, eggs, lemon zest, lemon juice, flour, and baking powder.
Pour the filling onto the baked crust, and bake for another 20 minutes.
Let the lemon bars cool completely.
Use the parchment overhang to remove the lemon bars from the pan, and dust with powdered sugar.
Cut into 2-inch squares.