This is the recipe that I use for buttermilk pie and it is outstanding! You need:
9 inch pie pastry crust
1 1/2 cup granulated sugar
3 tablespoon all-purpose flour
1 cup buttermilk, divided
3 eggs, slightly beaten
1/4 cup melted butter
1 teaspoon pure vanilla extract
1/2 cup chopped pecans
Preheat oven to 425 degrees F. Prepare your pie pastry.
In a large bowl, combine sugar, flour, and 1/2 cup buttermilk. Add beaten eggs and the remaining 1/2 buttermilk; mix well with a whisk. Mix in the melted butter and vanilla extract.
Pour into prepared pie crust. Sprinkle pecans over the top. Bake for 10 minutes, then reduce heat to 350 degrees F. and bake approximately 25 to 30 minutes or until a knife inserted near the center comes out clean. Remove from oven and let cool on a wire rack.