1 whole garlic bulb, separated into cloves and peeled
3 medium leeks, white and light green parts only, cleaned and cut into 1-inch pieces
3 medium carrots, cut into 1-inch pieces
8 cups water
1/2 pound fresh mushrooms, quartered
1 cup packed fresh parsley sprigs
4 sprigs fresh thyme
1 teaspoon salt
1/2 teaspoon whole peppercorns
1 bay leaf
Heat oil in a stockpot over medium heat until hot. Add onions, celery and garlic. Cook and stir 5 minutes or until tender. Add leeks and carrots; cook and stir 5 minutes. Add water, mushrooms, parsley, thyme, salt, peppercorns and bay leaf; bring to a boil. Reduce heat; simmer, uncovered, 1 hour.
Remove from heat. Strain through a cheesecloth-lined colander; discard vegetables. If using immediately, skim fat. Or, refrigerate 8 hours or overnight; remove fat from surface. Broth can be covered and refrigerated up to 3 days or frozen up to 6 months.