When cooking mushrooms, many recipes tell you to remove the mushroom stems, but living a frugal lifestyle means I feel guilty tossing those stems away.
I used to cook them anyway, regardless of what the recipe said, but recently I started collecting the stems in a freezer bag. Then, when my mushrooms have been neglected and start to shrivel or develop bruises, I add those to the bag.
Once I have collected about 2 cups of shriveled mushrooms and stems, I place them in a sauce pot with s little salt, pepper, a couple of garlic cloves and cover it with water. Set the pot to simmer, covered, over medium heat and then reduce to medium-low once the water boils.
You can let the stock simmer as long as you want and add a little more water as needed. The longer the stock simmers and evaporates, the stronger your stock will be. I recommend at least an hour.
Pour the broth through a strainer and reserve the liquid, discarding the vegetables.
Then, you can freeze your mushroom stock or use it to make a homemade cream of mushroom soup, add to other soups, rice, or pasta instead of water, or use instead of chicken or beef stock substitute to make vegetarian dishes.