I recently made macarons an am now left with a surplus of egg yolks. Any ideas on how long they keep and how to use them?

Sabayon for all your friends.

ice cream! if you don't have an ice cream machine the process can be quite involved but nonetheless fun! or creme brule.

Custard, mayonaise, hollandaise, cake!

Try making custard with them

Before you freeze them, be sure to whisk them together. Otherwise, the membrane turns sort of chunky in the freezing process. It's also a good idea to strain them once thawed, than go ahead with whatever you decide to make with them.

You can freeze them, but you will need to add a fresh egg yolk to them when you thaw in order to get the consistency to return to normal.