Prepare Lemon Mixture:
In a bowl, combine the lemon slices, sugar, and salt. Cover with plastic wrap and let it sit undisturbed for 8–12 hours or overnight.

Preheat Oven:
When ready to bake, preheat your oven to 450°F (230°C).

Whisk Eggs:
Whisk the eggs until frothy.

Prepare Pie Crust:
Line a 9-inch pie pan with one pie crust. Brush the crust with some of the whisked eggs.

Mix Filling:
Pour the remaining eggs into the bowl with the lemon mixture. Add the flour and vanilla extract, then stir well to combine.

Assemble Pie:
Pour the lemon-egg mixture into the pie crust. Cover with the second crust, trim any excess dough, and crimp the edges. Cut a few slits in the top crust to allow steam to escape.

Bake:
Bake the pie at 450°F for 20 minutes. Then reduce the oven temperature to 400°F (200°C), cover the pie with foil to prevent over-browning, and bake for an additional 15–20 minutes.

Cool and Serve:
Let the pie cool for at least 2 hours before slicing. Serve with whipped cream or vanilla ice cream if desired.