Preheat the oven to 350°F (175°C).
Fit the single pie crust into a 9-inch pie dish and crimp the edges if desired.
Cover the crust with foil and fill with pie weights or dried beans. Blind bake on the center rack for 20 minutes, then remove the foil and weights and let the crust cool completely while leaving the oven on.
In a large bowl, whisk together the flour, cornmeal, and sugar until combined.
Add the vanilla, sour cream, buttermilk, lemon juice, and lemon zest to the dry ingredients and stir to combine.
Whisk in the melted butter and the lightly beaten eggs until the filling is smooth (a few small lumps are fine).
Pour the filling into the cooled pie shell and smooth the top.
Bake on the center rack for 50 to 55 minutes, until the center is set and a toothpick inserted near the center comes out clean.
Remove the pie from the oven and let it cool completely on a rack; the filling will continue to set as it cools.
If desired, top with fresh berries and dust with confectioners' sugar before serving.