Measure the flour into a large bowl. Whisk the salt and sugar into the gluten free flour.
Grate chilled butter then gently toss the shredded butter into the flour mix until it is evenly distributed throughout.
Add the beaten egg, gently work it in with your fingers until the mixture is crumbly. Do not overwork.
Add cold water one tablespoon at a time, working it in by hand until a moist, crum dough forms. The crumbles should compress in shape and stick when squeezed together. If it gets a little too sticky or wet, just add a bit more flour.
Shape the dough into a large ball. Cut the ball in half, set one half to the side. Place one dough ball onto a sheet of parchment paper that has been sprinkled with additional gluten free all purpose flour mix. Press with your hand to make a flat circle.
Sprinkle a small amount of gluten free flour mix over then covering with another sheet of parchment paper.
Roll out dough into a circle that’s about 2” wider then your pie pan.
Carefully peel off the top layer of parchment. Pick up the rolled pie crust by the under layer or parchment, center it over the pie plate, and flip it into your pan.
Slowly pull the bottom layer of parchment off of the pie crust. If the crust breaks apart at any point just pinch the dough back together in those spots.
Preheat oven to 350 degree.
With a mixer, combine sugar and softened butter.
Seperate your 3 egg yolks from their whites, set white aside.
Add yolks, and 1 egg to sugar/butter mixture, mix until well combined.
Add vanilla, buttermilk, and cornstarch and mixed on medium for 2 minutes.
Pour mixture into your pie crust and COVER crust edges with foil or pie crust covers.
Bake for 1 hour or until toothpick comes out smooth. Should not be liquidy, but firm like a custard.
Let cool before adding meringue.
Once your pie has cooled completely, turn your oven on broil.
Whisk your egg whites in a heavy duty mixer with 2 tablespoon powdered sugar until stiff peaks form about 4 minutes. Gently pour your whisked whites onto your pie and evenly spread with spatula. You can create peaks or leave it smooth, then place under the broiler for 2-3 minutes until golden brown color forms (be sure to WATCH, this can over brown very quickly!).