It is in her Nigellissima book. Apparently it is a modern classic Mark Hix recipe.
The berries are served frozen with the hot sauce poured over.
It sounds rather strange but also very nice and wondering if it is worth giving a go.
Here is the recipe www.nigella.com/cookbook-corner/view/morning-to-midnight-a-book-of-chocolate-recipes-for-the-whole-day-and-night-48