Yield: 1 1/2 to 2 quarts
2 teaspoons olive oil
2 large yellow onions, roughly chopped
1 leek, trimmed, cleaned, and roughly chopped
8 ounces button, cremini or shitake mushrooms, cleaned and halved
2 tablespoons tomato paste
2 carrots, roughly chopped
2 celery stalks, roughly chopped
4 garlic cloves
2 bay leaves
5 sprigs of thyme
6–8 parsley stems
Heat the olive oil over medium-high heat in a large, deep pot. Add the onions, leek, mushrooms, and tomato paste, and saute until the vegetables have begun to brown, about 5 minutes. Add remaining ingredients to the pot. Cover the ingredients with 3 quarts cold water and bring to a boil. Reduce to a simmer and let cook for for 1 - 2 hours. Add more water if it evaporates too quickly. Let cool for several hours.
Strain the stock, pressing down hard on the solids (particularly the onion, which will have absorbed lots of liquid). Store in the refrigerator or freezer.