How to Make It
Preheat oven to 425°. Fit 1 piecrust into a 9-inch metal pie pan according to package directions, pressing excess dough onto rim of pie pan. Cut shapes from remaining piecrust to use around pie edge. (We used a 1/2-inch round cutter.) Brush 1 Tbsp. buttermilk around pie edge; arrange shapes around pie edge, pressing to adhere. Brush shapes with 1 Tbsp. buttermilk. Prick bottom and sides of piecrust 8 to 10 times with a fork. Line piecrust with parchment paper, and fill with pie weights. Bake 15 minutes.
Whisk together pumpkin, next 6 ingredients, and remaining 1 1/2 cups buttermilk in a large bowl. Pour mixture into piecrust.
Bake at 425° for 10 minutes. Reduce heat to 325°, and bake 35 to 40 more minutes or until edge of filling is slightly puffed and center is slightly jiggly. Cool on a wire rack 1 hour. Store in refrigerator up to 2 days.