I bought a large ceramic stone at my local egg supply store to try pizza. Not wanting to put too much effort into making my own just yet, I bought two frozen pizzas. The first effort was cooked on the stone with the thermometer temp at 400 or so & needless to say it burnt quite quickly. I cut the temp in half for the second one, but it still burns on the bottom at 200 degrees. What's the pizza cooking secret that doesn't blacken/burn the bottom? Thanks.