Preheat the oven to 350 degrees F. Grease an 8-inch square baking dish with butter.
For the crust: Combine the flour, butter, sugar and salt in the bowl of a food processor; pulse to combine. Pat the crust into the prepared baking dish, leaving a small lip around the edge to hold the filling. Place in the oven and bake until slightly golden, 10 minutes.
For the filling: In a small bowl, combine the eggs, lemon zest, lemon juice, flour, sugar and salt; whisk together, then pour over the crust. Bake until the filling is firm and the crust is golden brown, 20 minutes.
Let cool for 30 minutes, then chill in the refrigerator until the filling is firm and has set, 1 hour.
Remove the lemon bars from baking dish and dust with confectioner's sugar. Cut into 16 squares. Arrange on a platter and serve.