- 3 pounds mushroom stems and other scraps
- Salt and freshly ground black pepper to taste
- Preheat the oven to 350°F.
- Spread the mushroom stems and scraps on an ungreased baking sheet. Roast for 20 to 30 minutes, or until lightly browned. Turn the mushrooms once or twice during roasting to promote even browning.
- Transfer the mushrooms to a large stockpot and add enough cold water to cover the mushrooms by 2 inches. Bring to a boil over high heat, reduce the heat and simmer for about 1 hour.
- Strain the broth through a fine-mesh sieve into a bowl. Press on the solids with the back of a spoon to extract as much liquid and flavor as possible. Discard the solids.
- Return the broth to the pot and bring to a boil over high heat and cook for about 20 minutes until reduced by half.
- Remove from the heat and season with salt and pepper. Cool in an ice-water bath. Use now or cover and rdrigerate for up to 3 days or freeze for up to 2 months.