How am I supposed to heat a pie-iron-style pizzelle iron? I found an old pizzelle iron in one of my cabinets. It looks like this: 

Most of the pizzelle recipes I found — for example this one — are for a "George Foreman"-style pizzelle iron, and are self heating. What should I use to heat this pie-iron stlye pizzelle iron? An open fire?
It is not originally for camping but for using with a real flame or fire.  Used it for years. It is the only kind I have.  Works great on gas stove burners.