Rehydrate the Porcini: Place the dried porcini mushrooms in a heatproof bowl and cover with 3 cups (720 ml) of very hot water.
Let them soak until soft, about 20-30 minutes.
Sauté Vegetables: While the mushrooms soak, heat the olive oil in a large pot or Dutch oven over medium-high heat.
Add the fresh chopped mushrooms and sliced carrots.
Cook, stirring occasionally, until they are nicely browned and caramelized, about 8-10 minutes.
Don't rush this step; the browning builds flavor!
Toast the Barley: Add the rinsed barley to the pot.
Cook, stirring frequently, for about 5 minutes until it becomes fragrant and lightly toasted.
Season generously with salt and pepper.
Prep the Porcini: Once soft, lift the porcini from their soaking liquid, squeezing out any excess water. Coarsely chop them. Carefully pour the soaking liquid through a fine-mesh sieve into a separate container, leaving behind any grit at the bottom of the bowl.
Reserve this flavorful liquid.
Combine and Simmer: Add the chopped porcini to the pot and stir for one minute.
Pour in the reserved mushroom soaking liquid, the mushroom stock, and add the bay leaf.
Bring the soup to a boil, then reduce the heat to low, cover, and let it simmer for 20-30 minutes, or until the barley is tender and cooked through.
Finish and Serve: Remove the bay leaf and stir in the soy sauce.
Taste the soup and adjust the seasoning with more salt and pepper if needed. Ladle into bowls and serve hot.
Don't discard the mushroom soaking liquid! It's packed with umami and is the secret to a deeply flavorful broth. Just be sure to pour it off carefully to leave any sediment behind.
Using a variety of fresh mushrooms, like shiitake, cremini, and portobello, will create a more complex and robust flavor profile than using just one type.