01 - Fill a medium saucepan with approximately 2 inches of water. Bring to a gentle simmer over medium heat, ensuring bubbles are small and consistent rather than a rolling boil.
02 - In a large, heatproof mixing bowl, combine egg yolks and granulated sugar. Whisk vigorously until the mixture becomes pale yellow and slightly thickened, approximately 2 minutes of active whisking.
03 - Place the heatproof bowl over the simmering saucepan, creating a double boiler setup. Verify that the bowl's bottom does not make direct contact with the water surface.
04 - Slowly drizzle the Marsala wine into the yolk mixture while whisking continuously. This gradual incorporation prevents the eggs from scrambling and ensures emulsification.
05 - Maintain steady whisking motion for 8 to 10 minutes. The custard is ready when it has tripled in volume and forms thick, soft ribbons that hold their shape briefly when the whisk is lifted.
06 - Remove the bowl from the double boiler. Quickly portion the warm zabaglione into individual dessert glasses or serving bowls for immediate presentation.
07 - Top with fresh berries or arrange ladyfingers and biscotti alongside for dipping, if desired. These additions complement the wine flavors and provide textural contrast.