Prepare the Crust: Pre-bake your pie crust according to its recipe directions.
Once baked, reduce the oven temperature to 350°F (175°C) and let the crust cool slightly on a wire rack.
Warm the Dairy: In a small saucepan, gently heat the buttermilk and cream over medium-low heat until it is steaming but not boiling.
Mix the Base: In a separate large bowl, whisk together the 4 whole eggs, 2 egg yolks, sugar, salt, and vanilla extract until smooth and combined.
Temper the Eggs: While whisking continuously, slowly and gradually pour the hot buttermilk mixture into the egg mixture. This tempering process prevents the eggs from scrambling.
Assemble the Pie: Pour the custard filling into the slightly cooled, pre-baked pie crust. Evenly scatter the fresh blueberries over the top; they will float as it bakes.
Bake the Custard: Carefully place the pie in the preheated oven.
Bake for 35 to 45 minutes, or until the edges are set but the center still has a slight jiggle. The pie will continue to set as it cools.
Cool and Chill: Remove the pie from the oven and let it cool completely to room temperature on a wire rack.
Once cooled, cover and transfer to the refrigerator to chill for at least 2 hours before serving.
Don't overbake! The pie is ready when the center still jiggles slightly. It will firm up perfectly as it cools.
