"Farro Pasta with Mushroom Ragu & Walnuts"

Ingredients

• 3 cups vegetable stock
• 1 leek, coarsely chopped, or 1 small onion, halved
• ½ cup dried porcini mushrooms, crushed up or chopped
• A few slices of lemon
• 1 bay leaf
• 4 tbsp. olive oil
• 1 lb. fresh mushrooms (such as cremini), wiped clean and sliced
• 2 tbsp. fresh thyme, chopped
• 1 rib celery with leafy top, finely chopped
• 3 large shallots, finely chopped
• 4 cloves garlic, chopped
• Salt
• pepper
• 1 cup white wine
• 1 lb. farro spaghetti
• 1 cup walnuts, toasted and chopped
• 1 cup grated Pecorino Romano
• ½ cup fresh flat-leaf parsley, finely chopped