If time allows, it is safest to cool the soup before pureeing it. If you re in a hurry, at least cool it to not much more than body temperature. To reduce the chance of spattering, pulse the blender on and off a couple of times before leaving it on, and hold the top down until you re sure it s not going anywhere. Although it was the arrival of spring and fresh local vegetables that made me consider soup, two of the recipes here are just as good with frozen vegetables. I would happily use frozen peas, given the labor saved.
Frozen spinach tastes nearly as good as fresh, although it doesn t save much time or effort.
But frozen asparagus is simply not as flavorful. Combine spinach, onions and stock in a saucepan, and turn heat to medium high. Bring to a boil, and lower heat so mixture barely bubbles. Cook, stirring occasionally, until spinach is very tender, about 10 minutes. Turn off heat, add nutmeg and a sprinkling of salt and pepper, and let cool at least a few minutes.