In the bowl of a standing mixer (or with a hand beater), whisk eggs until frothy.
Add sugar and flour to the bowl and beat to combine. Scrape the sides and bottom of the bowl well to ensure even mixing.
Beat in the melted and cooled butter.
Add buttermilk, lemon juice, lemon zest, and vanilla extract to the bowl and beat 1 minute longer.
Pour the prepared filling into a 9” unbaked pie crust.
Bake for 35-40 minutes, or until the center of the pie is nearly set (the pie will be just slightly jiggly throughout, but the center should not be runny). Cover the edges of the pie crust after the first 15-20 minutes (once they are golden brown) to prevent the crust from burning.
Cool pie completely before slicing and serving.
Serve with fresh whipped cream.
Sometimes people add a bit of nutmeg and/or bourbon/rum to the buttermilk pie.
Buttermilk pie is similar to a chess pie, but a chess pie includes cornmeal and typically vinegar. Buttermilk pie has a consistency closer to custard.