• Coarse sea salt
• 3/4 cup farro
• 4 small fresh porcini mushrooms
• 5 tablespoons extra-virgin olive oil
• 1 celery stalk, finely chopped
• 2 tablespoons finely chopped onion
• 1 garlic clove, peeled
• 2 ounces dry white wine
• 4 cups water, heated to a simmer
• 2 teaspoons tomato paste, preferably double concentrated
• 1/2 teaspoon finely chopped fresh rosemary
• Freshly ground black pepper
• 3/4 pound mussels (preferably cultivated), scrubbed and beards removed
• 1 tablespoon unsalted butter
• Whole parsley leaves, for garnish
   

Bring a large pot of salted water to boil. Add farro and cook until al dente, about 18 minutes. Drain and spread on a large plate to cool.

Trim mushrooms and cut stems from caps. Separately cut stems into 1/4-inch dice and caps into 1/4-inch-thick slices.

Heat 3 tablespoons oil in a large pot over medium-high heat. Add celery, onion and garlic; reduce heat to medium and cook, stirring frequently, until softened, about 5 minutes. Remove and reserve garlic.

Stir in farro; cook 1 minute more, then add 1 ounce wine and cook until evaporated. Add water and tomato paste; stir to combine. Bring to a simmer, then remove from heat and cover to keep warm.

Heat 1 tablespoon oil in a large nonstick skillet over medium-high heat. Add mushroom caps and stems, reserved garlic, rosemary and pinch salt and pepper. Cook until mushrooms are golden. Add mushroom stems to soup. Transfer caps to a plate; leave garlic in skillet.

Add remaining tablespoon oil to skillet; heat over high heat. Add mussels, remaining ounce wine, and pinch salt and pepper. Cook, covered, until mussels just open wide, checking frequently after 2 minutes and transferring opened mussels to a bowl. (Discard any mussels that remain unopened after 6 minutes.) Pour liquid from skillet into soup.

Remove mussels from all but 8 shells; stir shelled mussels into soup. Heat soup to a bare simmer; whisk in butter. Adjust seasoning. Ladle soup into bowls. Garnish with remaining mussels, mushroom caps and parsley.