Oven helper. Black steel/stone in bottom of 3 Big ingredients oven.

Hi there. I think you might be talking about a pizza stone or baking steel—a tool that provides an evenly heated cooking surface for pizza as well as other baking projects. We sell a few of them in our shop (like this one here: https://food52.com/shop/products/3817-emile-henry-ceramic-pizza-stone). Hope this helps.