Chicken Tetrazzini - Lidia

Ingredients

• 5 tablespoons butter, plus more for the baking dish
• 1 1/2 teaspoons kosher salt, plus more for pasta pot
• 2 1/2 cups chicken stock (see here)
• 4 tablespoons extra-virgin olive oil
• 1 pound white mushrooms, sliced
• 6 fresh sage leaves, chopped
• 1/4 cup all-purpose flour
• 3 cups milk
• Pinch freshly grated nutmeg
• 1/2 head broccoli, in small florets
• 1 pound linguine, broken in half
• 4 cups shredded or chopped leftover cooked chicken, without skin and bones
• 1 cup grated Grana Padano or Parmigiano-Reggiano
• 1/4 cup dry bread crumbs