Instructions: 1. Boil potatoes and pinch of salt in water to cover until very tender, about 30 minutes. Drain; cool for easy handling and peel.

2. Combine 1 cup sugar, lime zest and 1/2 cup water in a heavy saucepan.

Heat to a boil over medium heat until sugar dissolves, about 5 minutes.

Cool; discard zest.

3. Put egg whites, sugar, 1 tablespoon water and cream of tartar in top of double boiler over gently simmering water. Cook, whisking constantly, until temperature reaches 160 degrees. Whisk vigorously so the whites dont coagulate. (They will turn white and foamy; this is ok.) Transfer to mixer bowl; set aside.

4. Combine sweet potatoes and cooled syrup in food processor. Pulse until smooth. Pour mixture into top of double boiler over gently simmering water.

Stir in egg yolks, rum, mace, ginger and bitters. Stir until mixture thickens, about 10 minutes. Cool.

5. Beat egg whites until stiff peaks form, about 3 minutes. Fold into sweet potato mixture in thirds. Cover and freeze. To serve, remove from the freezer and allow to soften slightly.

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