Preheat oven to 350 degrees F. Place pecans on a cookie sheet and toast for 8-10 minutes or until aromatic. Let cool, then chop coarsely.
Reduce oven heat to 300 degrees F.
In a mixing bowl, beat together butter and both sugars. Beat in vanilla and eggs; Stir in flour and salt. Add buttermilk and stir until fully incorporated. Stir in pecans. Pour into pie shell.
Place in oven (set on a cookie sheet to catch drips) and bake at 300 for 1 hour and 15 minutes. Cool completely, then chill.