1 large onion (about 1/2 pound), peeled and quartered
1 3-inch piece of fresh ginger
3 quarts water
1 pound leeks (1 1/2 large), tough ends cut away, halved lengthwise, cleaned and cut in thick slices
2 medium turnips (about 10 ounces), peeled and cut in wedges
1 pound carrots (3 large), peeled and sliced thick
2 ounces mushroom stems (from about 8 ounces mushrooms), or 4 dried shiitakes
1 head of garlic, cut in half
2 stalks lemon grass, trimmed, smashed with the side of a knife, and sliced
Salt to taste
1 to 1 ½ tablespoons sugar (to taste), preferably raw brown sugar
6 star anise pods
5 whole cloves
1 tablespoon black peppercorns
1 2- to 3-inch cinnamon stick
1 to 2 tablespoons fish sauce (nuoc mam), to taste (optional)