Place a baking sheet onto the middle rack of the oven and preheat it to 350 degrees F.
Lay the pie crust over a rolling pin and guide it onto a greased glass pie plate.
Gently press the bottom and sides of the pie crust into the pie plate. (If there is a lot of pie dough, overhang trim excess with a sharp knife). Prick the base of the pie crust with a fork.
Crimp the edges of the pie crust and place the pie plate in the freezer for 20 minutes.
In a large bowl, combine the sugar, cornmeal, flour and salt. Whisk until combined.
Whisk in the eggs, yolks, and lemon juice until incorporated. Then, add the buttermilk and melted butter and continue whisking until smooth.
Transfer the filling to the pie crust and place the pie plate on the baking sheet in the oven.
Bake for 30 minutes, cover with aluminum foil, and continue baking for another 20 minutes.
Remove the pie from the oven and place it on a wire rack to cool to room temperature. (It should still have a bit of jiggle.) Then, place the pie in the refrigerator and chill for one hour.
Just before serving, dust with the powdered sugar.