Sweet Potato Buttermilk Pie

Bake sweet potatoes in a 400 degree oven for 1 hour. Let cool 10 minutes and then peel the skins off.

Be sure to place the sweet potatoes on a baking sheet when you bake them. They can ooze and make a mess on the bottom of the oven. This step can be done up to 48 hours in advance.
Place sweet potatoes in a bowl and mash well with a fork. Measure out 1 1/4 cups of mashed sweet potatoes. If you want to make sure it is smooth, you can use a hand-held mixer to get the sweet potatoes really smooth and creamy.
Preheat oven to 450 degrees. Unroll pie dough and place in a 9-inch pie plate. Shape to fit and crimp the edges. Prick bottom and sides with a fork.

Bake for 9 to 11 minutes. Let cool. Reduce oven temperature to 375 degrees.
Place the 1 1/4 cups sweet potato in a medium bowl. Add melted butter, lemon juice, nutmeg, cinnamon, and salt and stir until smooth.
Whisk egg yolks until thick and pale in a large bowl. Add sugar and brown sugar and whisk for 1 minute.
Add sweet potato mixture to egg yolk mixture and whisk until smooth.
Whisk in flour 1 teaspoon at a time.
Whisk in buttermilk.
Using an electric mixer, beat egg white until soft peaks form. Gently fold egg whites into batter.
Pour batter into pie crust. Bake at 375 degrees for 35 to 40 minutes.