1. Put egg yolks, sugar, sherry, zest, and juice in a medium metal bowl; set over a pot of simmering water (water shouldn't touch bowl). Whisk mixture constantly until fluffy, lighter in color, and very warm, 3 to 5 minutes. Remove from heat; nestle into a bowl filled with ice water.
2. Whip egg whites with a mixer, adding vinegar when they start to look foamy, about 30 seconds. Continue to whip until soft peaks form. Fold cool yolk mixture into whites until no streaks remain. Serve with berries.
*Instead of raw eggs, you can use pasteurized eggs, available at well-stocked grocery stores.