Preheat the oven to 350 degrees F. Fit the pie crust into a standard 9" pie plate, and keep it in the refrigerator while you make the filling.
In a large bowl, whisk to combine the sugar, buttermilk, eggs, melted butter, Meyer lemon juice, Meyer lemon zest, vanilla extract, and salt, until thoroughly blended and smooth.
Add the flour and briefly whisk until incorporated.
Pour the filling into the unbaked pie crust and bake for 60 minutes, until the top is golden brown and crackly. To further assess doneness, jostle the oven rack slightly and look at the filling. The custard should jiggle when moved, but shouldn’t look liquidy or loose in the center.
Let the pie cool for at least 45 minutes before serving. Note that while the pie cools, it will deflate slightly, and this is normal because of all the eggs in the filling. When cooled, slice and enjoy!
*You may also use standard lemon juice and zest here, or do a 50/50 combination of lemon and orange.