Before hand, chill 4 serving cups (I like using cocktail glasses).
Bring 2-3 inches of water in a medium saucepan to a steady simmer.
In the meantime, take each chilled glass and dip the rim into a small bowl of tap water, and then onto a plate strewn with sugar (each glass will have a sugar rim!). Divide the strawberries evenly and out in cups.
Whisk the egg yolks and sugar together in a glass, heat resistant bowl until frothy.
At this point the water should be simmering and emitting a continuous flow of steam. Place egg yolk mixture in glass bowl on top of simmering pan, creating a double boiler. Whisk continuously. Make sure the bowl and water do not touch and that the yolk does not cook. Whisk in the marsala wine a little at a time until mixture doubles or triples in volume over heat. This should take about 5 minutes of whisking (a good workout!). It is done when the consistency becomes a soft mousse. If you are having trouble or your arm gets tired, you can also use a hand held mixer. Immediately spoon the zabaglione over the strawberries and serve.