Preheat the oven to 375°F.

On a lightly floured surface, roll the piecrust into a 12-inch circle. Transfer to a 9-inch pie plate (no more than 1 ¼-inch deep). Tuck the edges under and crimp as desired. Freeze for 20 minutes. Prick the bottom of the crust 8 to 10 times, all over, with a fork.

Line the frozen pie crust with parchment paper and fill with pie weights. Place on a rimmed baking sheet. Bake just until the edges of the crust are dry, 10 to 12 minutes. Carefully remove the paper with weights. Return to the oven for 3 to 5 minutes until the bottom of the crust is dry and the edges just start to turn light brown. Let cool slightly. Reduce the oven temperature to 350°F.

In a medium bowl, whisk to combine the melted butter and sugar. Whisk in the eggs, then flour. Add the buttermilk, lemon juice, lemon zest, vanilla, and pinch of salt and mix to combine.

Carefully pour the filling into the crust. Bake until the edges and center of the pie are set completely, 45 to 50 minutes. (Tent the pie with foil towards the end if either the crust or surface of the pie look darker than golden brown.) Let the pie cool completely, about 2 hours. Sprinkle with powdered sugar, if you like.