This is the same technique the tiramisù a few pages back borrows its base from, just served on its own instead of folded into anything -- egg yolks and sugar and Marsala, whisked over gentle heat until they turn into something closer to warm, drinkable custard than anything resembling plain eggs.
Serves 4.
Whisk the egg yolks and sugar together in a heatproof bowl until pale and slightly thickened. Set the bowl over a pot of gently simmering water, making sure the bottom doesn't touch the water directly.
Whisk in the Marsala gradually. Continue whisking constantly -- not occasionally, constantly -- until the mixture roughly triples in volume, turns pale and airy, and briefly holds a ribbon when you lift the whisk, about eight to ten minutes.
Pour into glasses immediately, and serve warm, with biscotti for dipping or a few fresh berries scattered on top.
If the mixture scrambles instead of staying smooth, the heat was too high, or the bowl was touching the simmering water directly rather than sitting above it. If it stays thin and never builds real volume, it wasn't whisked constantly or vigorously enough, or the heat was too low to properly cook and expand it. And if it tastes eggy rather than rich and custardy, it simply needed more time over the heat -- keep whisking, and trust the full eight to ten minutes rather than pulling it early.