The beef stock in this classic Italian dish needs a lot of time to simmer, but the flavorful result is worth the effort. This recipe makes enough stock for the tortellini soup plus two other delicious soups. Storage tip: Let the extra stock cool completely. Cover and refrigerate for several hours or overnight. Before using the stock, lift off and discard the fat on the surface. The stock will keep in airtight containers in the refrigerator for up to 3 days or in the freezer for up to 3 months.