•Let the cooked mushrooms cool to room temperature. Transfer the cooled mushrooms into small freezer containers. I recommend no larger than 1-cup size containers because really, how many cooked mushrooms are you going to use in most recipes?.
•Alternatively, put the mushrooms into freezer bags in a layer not more than 1/2-inch thick. Store the freezer bags horizontally. What you'll end up with is a frozen mushroom "pancake" that you can easily break up into pieces and take out only what you need.