What's the best way to interview UI/UX candidate?

[aihui]

I'm a rails developer, not designer. I plan to revamp my site (http://lovewithfood.com) to accommodate a fluid design for web, tablets and mobile. What's are the best ways you've used to interview UI/UX candidates? Is looking at their past portfolio enough?

[IVirOrfeo]

That's part of it, but you also have to know why you are hiring them. Think about your site,too many moving items. The bar on the bottom makes one feel claustrophobic. Show them your site beforehand; have them take a look at it in front of you, and ask them what they think of it. and why are you designing for non-widescreen monitors? Who has the money? not them.