Just wanted to pass on a reminder. When you blanch the asparagus (and this applies to all green veg, really), by all means, use plenty of boiling water (salted if you can), and don’t put too much asparagus in the pot at once. Last week I absent-mindedly dumped all of my chopped asparagus into the pot at once, which makes the water temperature plummet. As the water struggles to return to a boil, the asparagus suffers. Specifically, its color fades. You’ll notice in the picture that the asparagus on the left is a little closer to army green than you’d like. The asparagus on the right was blanched in batches and retained its color, since the water maintained a rolling boil throughout. (I’m not much of a photographer and the colors aren’t exactly true to life; you may just have to take my word on all this.)
For chilled asparagus (or pea) soup, shock the vegetables in an ice bath immediately after pulling them from the boiling liquid. Shocking sets the color, which is very important in a dish like this. And if the blanching liquid is part of the recipe, let it cool before you combine it with the asparagus to puree. Heat is the enemy of chlorophyll, and so this cool-down phase will help keep the finished soup green as spring itself.