Roll out the pie pastry on a lightly floured surface into an 11-inch (28cm) circle. Transfer it to a 9-inch pie plate. 1 x 9-inch unbaked pie crust
Trim any excess dough, leaving about ½ inch of overhang. Roll the overhanging dough under itself to make a thick border, then crimp the edges using your fingers.
Chill the crust for at least 20 minutes while you preheat the oven to 400°F (200°C).
Prick the bottom of the chilled crust all over with a fork. Line it with parchment paper and fill with pie weights or dried beans.
Bake at 400°F (200°C) for about 15 minutes, until the edges are lightly browned.
Carefully lift out the parchment and weights. Return the crust to the oven for 2 to 3 minutes, until the base no longer looks wet. Cool to room temperature.
Make the filling
Lower the oven to 350°F (180°C).
In a large bowl, whisk together the sugar, cornmeal, flour, salt, and nutmeg until evenly combined with no lumps. 300 g granulated sugar, 15 g cornmeal*, 12 g all-purpose flour, 1/2 tsp salt, 1/4 tsp ground nutmeg
Add the melted butter, buttermilk, lemon juice, and vanilla. Stir until smooth. 113 g butter, 113 g cultured buttermilk, 15 g lemon juice, 1 ½ teaspoons vanilla paste
In a separate bowl, lightly beat the eggs with a fork. Whisk the eggs into the filling until just combined but don't overmix it. 4 large eggs
Bake
Pour the filling into the cooled, par-baked pie crust.
Bake at 350°F (180°C) for 45 to 50 minutes. After about 20 minutes, tent the edges with foil or use a pie shield to prevent over-browning.
The pie is ready when the top is golden brown and the center still has a slight wobble. It will continue to set as it cools. The center should jiggle as one set piece, like jelly, not slosh or ripple like liquid. It will continue to set as it cools.
Turn off the oven, crack the door open, and leave the pie inside for 20 minutes. Then transfer to a wire rack and cool completely to room temperature before slicing.
Notes
Both US customary and metric measurements are provided. Use the toggle to switch between the two.
*Cornmeal is finely ground dried corn kernels. It is NOT the same as cornstarch, and they cannot be substituted for each other.
For the cleanest slices, chill the cooled pie in the fridge for at least an hour before cutting.
Leftover pie keeps in the fridge for up to 4 days, wrapped tightly. It also freezes well for up to 2 months.
Use room temperature buttermilk and eggs to avoid the melted butter seizing up when you mix everything together.