Preheat oven to 300 deg f. In a mixing bowl, cream butter and sugar. Stir in eggs, flour, buttermilk, and vanilla. Pour into pie shell. Bake until knife tip comes out clean, about 1 hour and 45 minutes. Cool slightly before serving. Makes 8 servings each serving �10 calories, 14 gm fat, 92 mg chol, 180 mg sodium. Percent of calories from fat �0.6 %