In the glass bowl, whisk together (either by hand or with an electric hand mixer) egg yolks and sugar until pale yellow and creamy. Set on top of the pot of simmering water. Add marsala and continue to beat until custard forms soft mounds, 15 minutes or less. Note: this will foam up and double or triple in volume during cooking. Serve atop sliced fruit or plain cake (pound cake, angel food cake, etc.)