According to Eberron: Rising from the Last War:
Kalashtar sleep, but they don't connect to the plane of dreams as other creatures do. Instead, their minds draw from the memories of their otherworldly spirit while they sleep. As such, you are immune to spells and other magical effects that require you to dream, like dream, but not to spells and other magical effects that put you to sleep, like sleep.
Meanwhile, for dream pastries (Curse of Strahd, chap. 6):
A creature that eats one in its entirety must succeed on a DC 16 Constitution saving throw or fall into a trance that lasts for 1d4 + 4 hours, during which time the creature is incapacitated and has a speed of O feet. The trance ends if the affected creature takes any damage or if someone else uses an action to shake the creature out of its stupor.
While in the trance, the creature dreams of being in some joyous place, far removed from the evils of the world. The places and characters in the dream are vivid and believable, and when the dream ends, the affected creature experiences a longing to return to the place.
So what happens if a kalashtar eats a dream pastry? Obviously they don’t dream. Do they fall into the trance? If so, what do they experience?
Alternately put, does the dream pastry’s trance require the dream, or are trance and dream mechanically separate (though related)? If they are separate, what happens to a kalashtar when they eat one?
Best Answer
A dream pastry's trance is not sleep; it's a specific kind of trance. It's more like a drug trip than anything related to rest, so there's no reason it would necessarily work differently on creatures that don't sleep or dream (including Warforged, if you going to be looking towards an Eberron/Ravenloft crossover). A magically-induced hallucination isn't necessarily the same thing as sending your mind to the plane of dreams (or whatever your particular game's cosmology has), even if the item itself uses the word 'dream' to describe the experience.
That said, Kalashtar do dream, they just dream differently from most creatures. If a DM wanted to rule that instead of a normal joyous dream, they dream the memory of a peaceful time in the long past of the spirit that lives inside them, that wouldn't be wrong, but there's nothing in the rules about it one way or the other.