In a large bowl, whisk together the sugar, lemon juice, lemon zest, eggs, flour, salt, melted butter, and vanilla, until thoroughly combined and smooth.
Pour into pie shell and bake for 45 minutes, until top is set. (Keep an eye on the crust and use foil or a crust protector if you notice it over-browning.)
Remove from the oven and let cool completely.
Place in the refrigerator for at least 5 hours to fully set.
Cut into slices and serve!
Notes
Allow to cool completely and chill for several hours. It's critical that the pie cools completely before chilling and then chills for at least 5 hours before slicing, which ensures the filling solidifies properly.