Sweet Potato Pie

Preheat oven to 375°F. Pour 1 1/2 inches of water into a medium stockpot with a strainer basket and bring to a boil over medium-high heat. Add sweet potatoes, cover, and steam until fork-tender, about 20 minutes. Strain sweet potatoes, place in a large bowl, and let cool to room temperature. Mash them to a smooth puree with a fork or a potato masher (you should have 1 1/4 cups puree; discard any excess). Add butter, lemon juice, nutmeg, cinnamon, and salt, mixing after each addition.

In a small bowl, beat egg yolks lightly with a whisk for about 30 seconds. Add sugar and beat until they're a creamy lemon-yellow color, about 1 1/2 minutes. Add egg mixture to sweet-potato mixture and stir until eggs are thoroughly incorporated and filling is a consistent bright-orange color. Add flour a little at a time, stirring after each addition, until thoroughly incorporated. Add buttermilk and stir to incorporate.

With a clean, dry whisk and in a separate bowl, whisk egg whites to soft peaks, about 1 1/2 minutes. Gently fold egg whites into sweet potato — buttermilk mixture until thoroughly combined. Pour mixture into prepared piecrust and bake on middle rack of oven until the center is firm and set, 35 to 40 minutes.

Remove pie from oven and cool completely on a rack. Serve at room temperature with a scoop of Buttermilk Ice Cream on the side.