Step 1 is to acquire a brain. I'm not going to ask where you got it. Just get the brain.
Then, as Instructables member Inition advises, scan the brain of dubious provenance with an MRI machine. Use a 3D printer to create a latex mold and pour in the chocolate.
If you've ever wanted to experience eating another specific person's brain -- or even your own -- this is as close as it gets without leading to awkward conversations.
Link -via Boing Boing