If you have a deep, flat skillet, it is ideal for making this sauce. A dutch oven, a large pot, or just about any big pan will work. I am partial to using my biggest skillet for this sauce.
For this recipe, you'll want to cook the mushrooms first, remove them from the pan and then add them back into the sauce at the very end. It keeps them separate and slightly firm, creating a more meat-y taste and texture.