Sift the powdered sugar, flour and salt into a medium-sized bowl and set aside. NOTE: We strongly recommend you weigh your einkorn flour, if possible, for better accuracy. If you don’t have a scale, fluff the flour with a fork before you measure it in a cup.
In the bowl of a stand mixer fitted with the paddle attachment, blend the butter and vanilla for 1 minute. Add the sifted dry ingredients to the butter mixture and blend until everything is combined.
Wrap dough in plastic wrap and form into a disc. Let dough chill in the refrigerator for 10 minutes.
Press chilled dough into the bottom of a 9"- or 10"-pan with a removable bottom (a tart or spring-form pan). Spray a piece of foil large enough to cover the crust with cooking spray. Place over the crust, sprayed side down, and fill with pie weights or dried beans to keep the crust flat.
Blind bake for 15–18 minutes or until the crust is golden. Remove from the oven and cool on a rack for about 20 minutes then place in the fridge for at least 30 minutes to chill.
Preheat the oven to 400 degrees.
To a stand mixer fitted with the paddle attachment, add the sugar, flour, cornmeal and salt. Mix until well blended then add the eggs. Beat on high until fully incorporated. Mix in the melted butter, lemon zest and lemon juice.
Pour the mixture into the chilled crust. Add strips of foil to cover the edges of the crust so it does not burn.
Put the pie in the oven and bake for 10 minutes.
Turn the oven down to 300 degrees and bake for another 40 minutes. It is done when a knife comes out clean and the internal temperature (2" from the edge) registers 210 degrees.
One Last Thing
Save time by making the crust ahead and keeping it in the freezer for up to a month. When it’s time to bake a filling into it, take it out of the freezer to thaw—and voila!