In a medium bowl, cover the dried mushrooms with 2 cups / 475 ml of hot water and set aside to rehydrate for 1 hour.
Meanwhile, in a small saucepan, combine the barley with 1 cup / 240 ml of water, bring to a gentle simmer, and cook for 1. 5 to 2 hours, or until tender.
Once plump, lift the rehydrated mushrooms from their liquid, reserving the liquid.
Rinse the mushrooms thoroughly under running water to remove any grit, then finely chop them.
Carefully strain the reserved mushroom soaking liquid through a cheesecloth or a coffee filter into a measuring cup.
Add 1 cup / 240 ml of this flavorful broth to the simmering barley to infuse it with more flavor.
Wash and thinly slice the fresh mushrooms.
Peel and coarsely chop the onion.
In a large skillet over medium heat, melt the butter.
Add the onion and fresh mushrooms, and sauté until the onions are translucent and the mushrooms have released their liquid, about 7-10 minutes.
Stir the finely chopped rehydrated mushrooms into the skillet.
Season to taste with salt and freshly ground black pepper.
Cook for another 10-15 minutes, stirring often, until the mixture is fragrant and deeply savory.
When the barley is tender, add it along with any of its remaining cooking liquid to the mushroom mixture in the skillet.
Stir everything together well.
Cover, reduce heat to low, and simmer for 30 minutes, stirring occasionally to allow the flavors to meld beautifully.
Adjust seasoning if needed and serve warm.
Don't skip straining the mushroom liquid! That rich broth is flavor gold, but it often contains grit. A coffee filter or fine cheesecloth ensures a smooth, delicious result.
