Preheat and prep: Heat your oven to 350°F (175°C). Place the unbaked pie crust in a 9-inch pie dish. Crimp the edges.
Set the pie plate on a baking sheet to make moving it easier.
Mix dry ingredients: In a large bowl, whisk together the granulated sugar, brown sugar, flour, nutmeg, and salt until no lumps remain.
Add wet ingredients: Whisk in the melted butter, then add the eggs one at a time, whisking until smooth. Stir in the buttermilk, vanilla, lemon juice, and zest. The mixture should be silky and pourable.
Fill the crust: Pour the filling into the crust.
If you like, dust a tiny pinch of nutmeg over the top for color.
Bake: Bake for 45–55 minutes, until the edges are set and the center has a slight jiggle, like gelatin. If the crust browns too quickly, tent the edges with foil during the last 15 minutes.
Cool and set: Remove the pie and let it cool completely on a rack. The custard will finish setting as it cools.
Chill for at least 2 hours for the cleanest slices.
Serve: Slice and serve plain or with a dollop of lightly sweetened whipped cream and fresh berries.