Put the heavy cream and 2 tablespoons of the limoncello in a small saucepan, and heat it until just about to come to a boil, but not actually boiling.
Take the pan off the heat and add the white chocolate, then swirl the pan about so that it is all submerged.
Take the berries out of the freezer and arrange them in a single layer in a dish or plate that has a small lip (so that the sauce doesn't drip off later). Sprinkle with the remaining 2 tablespoons of limoncello and leave for 5 minutes, during which time you can swirl your white chocolate pan about every now and again to help the chocolate melt into the lemony cream.
Using a rubber spatula, gently stir the chocolate-cream mixture, still off the heat, until it's smooth, then pour it over the berries and serve immediately.
Reprinted from Nigellissima. Copyright (c) 2012 by Nigella Lawson. Published by Clarkson Potter, a division of Random House LLC. All rights reserved.