3 large sweet potatoes (1-1/2 pounds total),
cooked, peeled, and mashed
1 cup fat-free evaporated milk
3 large egg whites
1 prepared 9-inch pie shell, unbaked
Preheat the oven to 350 degrees F. Beat together the margarine, sugar, and salt in a large bowl. Add the egg yolk, lemon juice, lemon zest, and cinnamon; mix well. Stir in the sweet potatoes and milk; mix again.
Beat the egg whites to stiff peaks and fold them into the sweet potato mixture; pour into the pie shell.
Bake for about 40 to 50 minutes, or until a knife inserted in the center comes out clean. Cool and cut the pie in 8 equal slices.