Whisk the egg yolks, sugar, Marsala, and salt in a large glass bowl until blended. Set the bowl over a saucepan of simmering water, but do not allow the bottom of the bowl to touch the water. Whisk the egg mixture over the simmering water until it is thick and creamy, about 4 minutes. Remove from the heat.
Using a large rubber spatula, fold the melted chocolate mixture into the egg mixture.