Fill a large saucepan with enough water to come 2 inches up the sides of the pan, and bring to a simmer. In a large metal bowl, whisk the sugar, Marsala, egg yolks, and salt to blend. Set the bowl over the saucepan of simmering water (do not allow the bottom of the bowl to touch the water). Whisk the egg mixture constantly until it is thick and creamy and a thermometer inserted into the mixture registers 160 degrees F, about 4 minutes. Remove from the heat.