Espresso Zabaglione

Fill the double-boiler pan with enough water to come just below the bottom of the mixing bowl without touching it.
Remove the bowl, and heat the water to a steady simmer.
While the bowl is still cold, drop in the egg yolks, sugar, espresso, and Marsala, and whisk together until well blended.
Set the bowl over the gently bubbling water, and immediately start whisking at a moderate speed.
Beat the egg mixture with large strokes, frequently scraping the whisk around the sides and bottom of the bowl, to heat the zabaglione evenly (and avoid scrambled eggs).
Whisk steadily as the zabaglione expands into a frothy sponge, 5 minutes or longer.
When the sponge is very warm to the touch and thickened enough to form a ribbon when it drops back on the surface, take the bowl off the double-boiler pan.
To serve the zabaglione warm, quickly whip the cream (with a whisk or an electric mixer) until it holds soft peaks.
Ladle the zabaglione into tall glasses, spoon a dollop of whipped cream on the top of each portion, and serve immediately.
For a chilled dessert, set the bowl of warm zabaglione into a larger bowl partly filled with ice cubes and enough water to cool the inner bowl but not splash over.
Whisk for several minutes, until the zabaglione is cool to the touch.
Whip the cream until it holds soft peaks, and fold it into the cooled zabaglione with a large rubber spatula.
Cover the bowl with plastic wrap, and refrigerate for 2 hours or longer, then spoon it into glasses or dessert bowls.