According to some grammar rules it should be make, plural verb in both cases. Anyway I find a lot of people that use a singular verb (also George W. Bush during a speech).
Personally, I think a singular verb sounds better. But grammarians say a plural verb should be used instead and I think that doesn't make much sense... for example, I can't say "What are in the box", and that's why I don't like a plural verb in my examples.
"What makes you happy?" --- "My friends" ----- "So your friends are what makes you happy, and what makes you happy are your friends"
All your opinions will be appreciated. Thank you in advance.