There are two types of brain organoid protocols: guided and unguided.

The current unguided protocol is: unguided brain organoids
This protocol comes from the lab of Michael Hiede from Göttingen, and it was published in JoVE.

It was originally modified from the famous Lancaster et al Knoblich, 2013 paper Nature.

Later on the protocol was published with more details in Nature Protocols. Lancaster and Knoblich, 2014, Nature protocols.