You can buy commercially produced manioc flour at the supermarket or online. But it's interesting to see how it's traditionally prepared - the low tech way. Like couscous, manioc flour seems like something that would be difficult to make by hand.
The Perfect Pantry, an excellent blog by Lydia Walshin (with a nice section of Spanish/Latino recipes), recently featured a wonderful photo essay about a Brazilian woman making farinha de mandioca from scratch.
I was especially fascinated with the press made within a tree trunk, which required a huge stack of rocks to provide the necessary crushing force. So ingenious! The special toasting oven is also interesting.
It's comforting to know that we will still be able to enjoy farofa, even if we run out of fossil fuels someday.