For a deeper, toastier flavor, roast the asparagus at 400°F (205°C) for about 15 minutes before simmering. If the soup is too thin, simmer uncovered a few minutes; if too thick, add a splash of broth or water. Store covered in the fridge up to 4 days. If freezing, cool completely and freeze up to 2 months; thaw overnight in the fridge and reheat gently.