My favorite way is to start with a very vague design question, with no expectation of any predefined answer. Then I try to make it a discussion, see if the can

My favorite way is to start with a very vague design question, with no expectation of any predefined answer. Then I try to make it a discussion, see if the candidate asks more questions, pokes around, can think in terms of abstractions - I don't expect any of it to match my own thought process. Another question is to pick a project they've worked on, and ask them how would they do it if they were given a clean slate.