Make the pie dough: Whisk both flours, salt and sugar together in a medium bowl. Using a pastry blender or your fingertips, work in the butter until coarse meal forms and some small lumps remain. Starting with 3 tablespoons, drizzle cold water over the dough; quickly stir in the water with a fork or your fingers until the dough begins to clump together into a more uniform mass and becomes slightly sticky. If it’s still dry and crumbly, add additional water, 1 tablespoon at a time.
Divide dough in half and form 2 single flat, chubby disks; wrap each in plastic wrap and refrigerate for at least 1 hour and up to 1 day. Once chilled, work quickly to roll out one of the disks on a lightly floured surface until it’s about 11-12 inches round. Carefully transfer to a 9-inch pie plate and nestle gently into place. Leave 1-inch of overhang (if there’s a great deal of overhang, trim), then fold edges under and crimp. Freeze the remaining disk for a future pie!
Pre-bake the pie shell: Preheat the oven to 375F. Prick the bottom of the pie shell a few times. Line with parchment paper or aluminum foil and fill to the top with pie weights or dried beans. Bake for 20 minutes, or until lightly golden. Remove pie weights or beans along with parchment or foil and bake for an additional 8 minutes, or until the shell is nice and dry on the bottom.
Decrease the oven temperature to 325 F.
Make the filling: In a small bowl, whisk together the eggs, buttermilk and vanilla. In a separate small bowl, whisk together the melted butter and honey until combined. Pour the honey mixture slowly into the egg mixture, whisking constantly, until well combined. Fold in the flour and stir well.
Assemble: Place the pre-baked pie shell on a baking sheet for easy transport to and from the oven. Strain the honey filling and pour into the shell. Carefully place pan into the oven and bake until the filling is set, about 55 – 60 minutes. Cool for 1 hour, then sprinkle the top liberally with flaky salt (if you sprinkle the salt on while still too warm, it may just dissolve onto the top of the pie instead of remaining flaky and pretty). Serve room temperature – or cold the next day. Refrigerate and cover leftovers for up to 2 days.