Preheat your oven to 350°F. Line a 9x5-inch loaf pan with aluminum foil, allowing some overhang to lift out the bars later.

In a mixing bowl, combine all-purpose flour, granulated sugar, and salt. Rub in softened butter until the mixture resembles coarse crumbs. Press into the prepared pan, building up the edges slightly. Bake for 12-16 minutes until golden brown.

In a separate bowl, whisk together the large eggs, sugar, lemon zest, and salt until the sugar is dissolved. Stir in the freshly squeezed lemon juice, then add the additional flour until smooth and well combined.

Once the crust is ready, reduce the oven temperature to 325°F. Pour the lemon filling over the hot crust. Bake for 13-18 minutes until the filling is set with a slight jiggle in the center.

Remove the pan from the oven and allow it to cool on a wire rack. Once cooled, transfer it to the refrigerator for at least an hour to set properly before slicing. Dust with icing sugar before serving.