Preheat your oven to 450°F / 230°C.
In a large roasting pan, toss the leeks (or onions), carrots, celery, parsnip, potatoes, garlic, and mushrooms with the olive oil until everything is well-coated.
Roast for about 45 minutes, shaking the pan and turning the vegetables occasionally, until they are deeply browned and caramelized.
Don't rush this step—the color is where the flavor comes from!
Transfer the roasted vegetables to a large stockpot using a slotted spoon.
Add the parsley, thyme, 1/4 cup (960 ml) soy sauce, peppercorns, wine, a pinch of salt, and 2 quarts / 2 liters of water.
Place the now-empty roasting pan over a burner on high heat. Carefully pour in 2 to 4 cups (960 ml) of water to deglaze the pan, scraping up all the delicious browned bits from the bottom.
Pour this flavorful liquid into the stockpot.
Bring the stockpot to a boil, then reduce the heat to a gentle simmer. Partially cover and let it cook for 30 to 45 minutes, until the vegetables are very soft and the flavors have melded.
Strain the stock through a fine-mesh sieve into a large bowl or container, pressing firmly on the vegetables to extract every last drop of liquid.
Discard the solids.
Taste the finished stock and adjust the seasoning with more soy sauce, salt, or pepper if needed. Use immediately or let it cool completely before storing.
Don't peel your onions or carrots! The skins add a beautiful, deep color and extra nutrients to the stock.
Add a piece of dried kombu (seaweed) or a few dried shiitake mushrooms to the pot while simmering for an extra boost of umami.
Freeze the finished stock in ice cube trays for perfectly portioned amounts to add to sauces, grains, or for sautéing.
