1 prepared 8-inch graham-cracker crust
1 large egg white, beaten until frothy
For the Filling:
2/3 cup packed light-brown sugar
3 tablespoons all-purpose flour
3 large eggs
1 1/4 cups low-fat buttermilk, well shaken
3 tablespoons unsalted butter, melted
1/4 teaspoon salt
For the Raspberry Sauce:
1/2 pint (1 cup) raspberries
2 tablespoons granulated sugar
1/2 teaspoon lemon zest
Preheat oven to 350°. Place crust (in its pan) on a baking sheet. Brush crust lightly with some egg white; discard remainder. Bake until crisp and slightly darkened, 6 to 8 minutes. Set aside to cool.
Make the Filling: In a food processor, process sugar and flour until well combined. Add eggs; process until smooth. Add buttermilk, butter, and salt; process just until blended. Pour into crust.
Bake until filling is almost set but center still jiggles slightly when pan is gently shaken, 35 to 40 minutes.
Make the Raspberry Sauce: Combine raspberries, sugar, and lemon zest in a bowl. Lightly mash about half the raspberries with a fork. Let sit at least 10 minutes to allow juices to release.
Transfer pie to a rack; cool completely. Cover, and refrigerate at least 2 hours and up to 2 days. To serve, slice pie and drizzle slices with Raspberry Sauce.