Preheat the oven to 350 degrees. Place the piecrust into the oven and bake for 10 minutes.
Combine the sugar with the flour and cornmeal, if you’re using. Cream the butter. Add the sugar mixture to the butter and then stir in the eggs, salt, buttermilk, baking soda, vanilla extract and vinegar.
Pour filling into the partially baked piecrust and bake in the oven uncovered until brown on top and the custard has set, about 45-50 minutes.