Scheduling and managing events using Outlook.com calendar
UPDATE: I erased my previous post, as I played around a little more and you have to hit the right button in the calendar UI to get to a real picker for the timezone, otherwise it's just a search box that doesn't understand UTC.
If you only have the search box like I did when I started, there is a small blue link that lets you 'Browse time zones', from which you can then choose UTC like the typical Windows picker. It doesn't seem to want to give me that option again or I'd take a screenshot of it. But you have to type something in the box first that it can't find to give you that option: