Mimic lecturing on blackboard, facing audience
Do not assume that facing the audience is actually better.  It depends on the type of content.  For example, if you are explaining a diagram (detailed hydraulic system for instance), you want the audience to concentrate on that, not the presenter.  The audience is still getting plenty of stimulation by having a live human voice along with visual content.  You actually don't want the presenter to distract the eyeballs from the intricate content.  (I see this wrong often with recorded talks where the video operator concentrates on the podium versus the charts, or shows both but with inadequate scale to see the slide charts.)  If you are doing math (as opposed to history or literature), the content is more intricate and you should have the audience concentrating on the formulas, not the speaker.
Take some occasional time to address the class when that is appropriate.  Examples are a "sea story" about test performance or industrial application of the math.  But these will be a minor amount of time within a math lecture.
I mean, if you really wanted to, you could write backwards in grease pencil on plexiglass like in an old Navy combat information center.  But really what is the point.  People concentrate on the status (content), not the writer anyways.  The one advantage is that you don't have a body blocking part of the board.  I believe there are now electronic versions that would flip this around for you (or you can use an OHP).  But still I think you lose a lot from having a lot less screen space than board space (especially with sliding boards).  So, the small advantage of facing is at the loss of huge amounts of content physical space.