Roll dough on a lightly floured work surface. Roll to about 10-inches in diameter and about 1/4-inch in depth. Location pie plate upside down over the rolled dough to ensure it’s the size that is right.
Transfer dough to pie plate and firmly press to sides and the underside of plate. Cut excess dough leaving about 1/2-inch overhang all Fold overhang to the pie and flute the edges using a fork, or crimp together with your fingers. Cover pie dough with plastic wrap and let rest in the fridge while you prepare filling.
Preheat oven to 350 degrees F. In a big bowl, whisk eggs, yolk and brown sugar together . Add flour, buttermilk, melted butter, vanilla, and cinnamon. Whisk until combined. Pour into prepared pie shell.
Bake for 40-50 minutes until center of pie is jiggly and set. Remove from oven and permit to cool on wire rack to room temperature. Instead, shop pie in refrigerator to cool quicker. Serve with whipped cream.
Pulse together flour, salt, and sugar in a food processor. Add cold butter a few cubes at a time with all the food processor. After mixture is crumbly, cease the device and like sand that is rough in feel. Add 2 tbs of water and yolk. Pulsation to get a couple seconds until dough starts to come together. Add another tablespoon of plain water if dough is too dry. Remove from machine and end kneading on a lightly floured surface. Flatten dough into a disc and wrap in plastic wrap. Cool for 10 minutes in the fridge for 20 minutes or freeze.