I buy mushrooms in a large quantity at a favorite discount gourmet store (they buy from the grocery warehouses that didn't manage to send all of their stock to grocery stores). So when I can find them I slice them, then saute in butter and package them in plastic restaurant carryout containers (poor man's Tupperware) and into the freezer. I usually package maybe a 1/2 cup in each container so pull them out in multiples if I need more. They're very soft, but they work on the pizza.