Mushroom Stock

Combine the dried porcini, dried shiitake, and kombu in a large pot and pour over the cold water. Leave to cold-infuse at room temperature for at least 30 minutes, or refrigerate overnight for a deeper, cleaner result. Cold-steeping draws out the glutamates gently, without the bitterness that rapid boiling can extract from dried mushrooms. The kombu should soften from a rigid black sheet to a supple, slippery frond — pull it out before the stock comes to a boil, as it turns bitter and slimy if cooked at a hard simmer.

Remove and reserve the kombu. Add the halved onion (with its papery skin — the skin deepens the color to a rich amber), the celery, crushed garlic, thyme, and cracked peppercorns. Bring to a bare simmer over medium heat — small bubbles rising steadily, the surface trembling but not churning. Simmer for 45 minutes. Do not boil hard: mushroom stocks turn muddy, bitter, and gritty at a rolling boil. A gentle simmer keeps the stock clear and the flavor clean.

Line a fine-mesh strainer with a piece of cheesecloth or a clean kitchen cloth and set it over a large bowl or pot. Ladle the stock through gently — do not press or squeeze the spent mushrooms and vegetables, as pressing forces bitter, starchy solids through and clouds the stock. Discard the spent solids. You can chop the rehydrated porcini and shiitake that plumped back up during cooking and use them in another dish — they are still full of flavor.

Taste the stock and season with fine salt, starting conservatively — most applications will add more seasoning from other ingredients. If using soy sauce, add it now: just a small amount deepens the umami and adds a warm, caramel complexity without making the stock taste Asian. It is optional but recommended for applications where color is not a concern. Store the finished stock in the refrigerator for up to 5 days, or freeze in measured portions for up to 3 months.