Preheat the Oven: Preheat your oven to 300 degrees Fahrenheit.
Cream the Butter and Sugar: In a large mixing bowl, cream together the sugar and unsalted butter until it's well blended and fluffy.
Add the Eggs: Beat in the eggs one at a time, ensuring the mixture is smooth after each addition.
Mix in Flavorings: Add the vanilla extract, a pinch of salt, and flour to the bowl, mixing until combined.
Incorporate Buttermilk: Slowly stir in the buttermilk until everything is thoroughly blended.
Prepare Pie Shell: Place the unbaked 9" pie shell on a lined baking sheet to catch any overflow.
Fill the Shell: Pour the buttermilk mixture into the pie shell, filling it just to the top.
Bake: Bake in the preheated oven for about 1 hour and 10 minutes or until the pie is set.
Cool and Serve: Remove from the oven and let it set until almost cooled before serving. Store covered in the fridge.