Preheat your oven to 350°F (175°C).
Cream together the softened butter and granulated sugar until light and fluffy. Gradually add in the flour and salt, mixing until combined.
Press the crust mixture evenly into the bottom of your prepared pan.
Bake in your preheated oven for about 15-20 minutes or until lightly golden.
In a separate bowl, beat together the four eggs until frothy. Then add in granulated sugar, flour, freshly squeezed lemon juice, and lemon zest. Whisk until smooth.
Pour the lemon filling over your pre-baked crust and spread it evenly.
Return the pan to your oven and bake again for an additional 20-25 minutes until the filling is set.
Allow to cool at room temperature for at least 1-2 hours or until fully set.
Dust with powdered sugar if desired before cutting into squares.