While this is not a book specifically about Ravenloft, some concepts fit very well with the setting (such as cursed fruits and rituals).
There is even a section featuring Ravenloft specific fruits, which can serve as hooks for horror adventures.
www.dmsguild.com/product/535416/Forbidd ... s-of-Power
Forbidden Fruits explores the magical fruits derived from Treants, expanding on the concept and presenting a wide range of abilities that characters can acquire by consuming them.
Sources of Power: The means by which Treant fruits grant specific powers.
Among the various types of fruits presented are:
16 Fruits with General Powers
6 Cursed Fruits
14 Ritual Fruits and the Fruits they produce
25 Fruits from specific Campaign Settings (4 from the Forgotten Realms, 4 from Eberron, 3 from Spelljammer, 1 from Greyhawk, 6 from Planescape, and 7 from Ravenloft).
A total of 61 Fruits of Power.
Additional details are also covered, such as soil, alternative uses, and the most diverse situations involving Treants and Fruits of Power.