Wash the outside of the lemon, being sure to scrub off any dirt. Slice the lemon and pick out the seeds. Using a food scale, weigh the lemon slices until you get 4 ounces. Place the 4 oz. of lemon slices into the bowl of a food processor. Discard any remaining lemon slices.
Add eggs, vanilla, salt and sugar to the food processor. Blend on high speed, about 20 seconds. Lower the speed and slowly pour the melted butter through the feed tube. Process the mixture until smooth.
Press one refrigerated pie crust into a 9" glass pie plate. Pour the lemon mixture into the pie crust. If desired, cut out shapes with the other pie crust using a cookie cutter. Arrange the shapes on top of the lemon mixture.
Bake 35 minutes, until the pie is set but still a bit jiggly. Cool at room temperature. Then, cover with plastic wrap and refrigerate until firm.