Preheat the oven to 350° Fahrenheit. Line an 8x8 pan with wax paper. Grease the wax paper generously with butter.
Combine 1 cup all-purpose flour, ¼ cup sugar and ¼ cup melted butter in a large mixing bowl. Mix with a wooden spoon until well combined. Press crust mixture into the lined pan. Bake for 15 minutes.
While the crust bakes, combine ½ cup lemon juice, 1 tablespoon lemon zest, 3 large eggs, 1 cup sugar3 tablespoon all-purpose flour in a large mixing bowl. Whisk until the mixture is completely smooth.
Remove the crust pan from the oven when done. Pour the filling on top of the crust. Return to the oven and bake for 20-25 minutes, until the filling no longer jiggles when pan is shaken. Remove the lemon bars from the oven.
Chill for at least 2 hours or up to 3 days. Remove from the pan and cut into 16 squares. Top lemon squares evenly with ½ cup powdered sugar to serve.