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1
Heat the oven to 175 °C. Line a 23 cm pie dish with the unbaked shell; trim and crimp the edge. Refrigerate the shell while the filling is prepared — the pastry should feel cold and firm to the touch.
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2
In a bowl, whisk together the sugar and eggs until the mixture is pale and the sugar has begun to dissolve — the ribbon falling from the whisk will hold its shape briefly before sinking back in.
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3
Add the melted butter, vinegar or lemon juice, cornmeal, and vanilla. Whisk until fully combined and smooth. The cornmeal will remain slightly granular in suspension; this is correct. The mixture should smell sharp and sweet together, the acid cutting clearly through the butter.
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4
Pour the filling into the cold shell. Transfer to the oven and bake for 40 to 50 minutes. This is where the dish lives or dies: the centre must jiggle as a single slow mass — like barely set gelatin — when the pan is gently shaken, while the top is golden-brown and crackled across its entire surface. An overbaked centre, one that does not move, will set rubbery rather than dense and creamy; an underbaked centre will never firm on cooling.
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5
Remove the pie from the oven and set it on a wire rack. Allow it to cool completely to room temperature before slicing — the custard continues to set as it cools, and the interior will feel firm yet yielding under light finger pressure at the edge.