How can I change the default font size for composing in Sparrow? I use Sparrow as my email client.

Recently, I sent an email with some wacky font sizes.  Now every time I compose a message, the default size is too small.  Even after I fix it, it reverts to the (small) size if I move the cursor to a new spot.

It seems like this would be an easy to find preference for default font and size, but I can't find the darn thing anywhere.  And it doesn't seem to be in Sparrow's online support.

I expect to be embarrassed by the answer, but can anyone point me to the right place?
I figured this out:  

I had a problem that my font got changed size 11, and changing back to 13 didn't fix the default - the next email would go back to 11

The solution is this: Type some text and highlight it.  But instead of changing the font in the pulldown above the editing window (which won't change the default), so this instead:

With the text selected, in the top menu select Format > Font > Bigger or Smaller, till it get the size you want.  (You can also do this by hitting Command + or Command -.)

Oddly, that fixes the default, while using the normal size toggle doesn't.