Stones were invented for pizzas, not for cookies. It must have been some serendipitous discovery that it even works for something with such a high butter content. As long as I have been baking cookies I have baked on a stone. I like it because the cookies bake so evenly, because the back of each cookie looks as good as the front, and I don't have some cookies getting too done while others on the same stone are too soft.
Almost everybody has at least one stone. Made popular by those kitchen shows you host right in your own home, I have found that almost every kitchen has at least one stone for pizza if not for baking. Being a bargain hunter, I have to plead guilty to buying several substandard stones (which I didn't learn were NOT such a bargain after baking on them). You can pick up a stone at Walmart, Kohl's, Williams Sonoma, Kitchen Collection, and Amazon. Having been invented for pizza, the thick crust is there to prevent anything from dripping through the stone so it really wouldn't matter if the stone is porous or not. But, when you put cookie dough on a stone, porousness matters. Cookie dough that begins with a pound of butter will bake beautifully and evenly on a stone when heated to 325 degrees. However, if you place your cookies on a porous stone that was intended to come into contact with pizza crust, you stand the chance of the butter dripping through, puddling up in the bottom of your oven, setting off your fire alarms, bringing firemen and firetrucks to the house and neighbors standing in the street. (Or so I've heard).
Recently, I embarked on a quest to find the best baking surface for cookies. I knew it would need to be a stone and it couldn't be porous. So, I googled up every stone on the internet I could find that was made in America and ordered one of each. All those stones arrived and I commenced using the scientific method to bake on each one until I could find the PERFECT stone surface for baking.
It is crazy that they all look alike! Some have handles, some are round, some are rectangle, some are square but the shape and size are the only things that appear to make a difference.....Then you bake on them.
If you lift the cookies off your stone and a little bit of cookie remains stuck to the stone, you have a substandard stone. That cookie tried to drip down into the pores of the backing surface but was unsuccessful.
If you lift the cookies off the stone and you can see the shape of the cookies you just baked, that butter dripped down into the pores in the shape of the Grinch and it stayed in that stone. Expect for that stone to eventually smell like rancid oil, especially when it gets hot.
If you immerse the stone in the sink because you want to clean it off, if the stone wicks up water, and mixes with that butter that is still inside the stone, when it gets dry, it is going to start growing a whole new science fair project on it. YUCK! (I keep this stone only to show my students what NOT to buy. No cookies have been baked on it since the mold started growing.)
So what does a good stone look like? How will you know if the stone you have is a good surface for baking cookies? Test it out. You don't typically get firetrucks until you have baked several rounds of cookies on it. This is my new favorite stone. It is 13" round. Yes, you can also bake pizza on it but I am personally a segregationist so I like to keep garlic and sugar apart. It is not porous so all of that butter stays in the cookie. I have baked at least 25 rounds of cookies on this stone and you see it looks the same as when I took it out of the box. When I get a brand new stone, I rub it with a butter wrapper the first time, then after that, I never season it anymore. The cookies do that for me. This stone will eventually turn a little darker but not a whole lot because we are not baking on a really high temperature. To clean, rinse with water and dry.This stone is made by American Bakeware (americanbakeware.com). The 13" is a real bargain compared to the home show. In fact, I can get almost two stones for the price of one rectangle. I have these available if you are local. If not, you can order online.
As always, if you like baking on metal, they are your cookies; do what you like. But if you are looking to up your cookie game, try baking on a great quality stone.