One questions which was asked me in similar flavors was:

How would you design an online shopping application like Amazon?

I get stumped with such questions because I don't understand where to start and which direction to take. In the previous interview I started with a high level technology stack I would use and then how the front end, middleware and database would be organized. They happened to be more interested in the Object modelling. I missed that.

In the recent interview I started with Object modelling, but they said they were interested in a high level tech stack I would go for and the reasons for each.

This makes me go a bit blank during interviews and I panic, blurting out 'Sorries' and 'I can't recollect it at this moment'.